If anything Spock appears to be speaking a Tolkienesque Elvish language.
Were Vulcans intended to be space elves or logical beings? It isn't reflected in their current language.
Is canon too well established for future writers to fix this logical gap in the description of the Star Trek universe?
The hyper-logical aspects of Vulcan society are recent (on their time scale) and their language still bears many of the same characteristics as the Romulan language. Both their peoples and their languages share a common ancestry.
The fact that the Vulcans speak this language proves that it is logical (as well as any marriage, or anything that a Vulcan does).
Jokes aside:
I am only aware of one Vulcan language that is fully fleshed out with a full grammar and vocabulary — Golic Vulcan from Mark R. Gardner and the now defunct VLI (not Marc Okrand; though some of his “gobbledygook” has been assigned discrete, concrete meaning in the Golic Vulcan lexicon). It is rife with features of organic human languages like archaic forms, irregular verb/noun pairs, nominalizing suffixes, adverbial clitics. It’s in no way designed to be unambiguously logical, but is quite pragmatically logical in that it easily supports a great deal of efficiency and aesthetic restraint. It is pro-drop so that unnecessary pronouns (and even the copula) are omitted when they are understood from context. Pervasive compounding via a head-final noun complex makes it extremely productive for incorporating new ideas and a similar function supports the verbalization of nouns via -tor. Plurals are not used if they don't add value in the relevant context. Nouns and verbs don't agree because they don't need to in order to convey sufficient meaning.
Fictional Vulcan civilization is full of art and culture with logic applied as an important layer in the overall mix, but logic is not the end-all-be-all. It is an idea and an ideal — one that helps very much with social justice (shila-kro’es), equality (ka’es), harmony (kril’es), and their sense of peace (sochya). Novel words that are relevant to technology and modern life are quite logically constructed as innovations. The main root in “computer” (tum-vel) is tum. It means “count”. Vel is a physical “thing”. A computer is a “counting thing”. The word for “abacus” is tum-nentu. There is tum again. Words like “garbage” (guhsh) and “fairy” (pu’a) have presumably been around for a very long time in their civilization, which has been literate for thousands of years. Those words don’t actually require the application of much logic to be useful or valid. Vulcans probably need to talk about garbage about as much as we do. But unless a member of Vulcan society is a researcher in ancient or alien cultures, fairies?, not so much. There is no reason for perfectly valid words to be abandoned or reinvented just for the sake of forced uniformity. Is it logical as a function of language to call a fairy a mapi’zaipos-glenon-ralasu (“tiny magical imaginary winged person”) just because you can if you already have pu’a as an option? Not really.
There is a lot of information on the Golic Vulcan language for those interested at http://korsaya.org.
Dif-tor heh smusma. Live long and prosper.
How would they be able to keep pace with the lesser, illogical races of the universe if they did?
The Sapir-Whorf (not that Worf) hypothesis states that ability to think certain thoughts may be limited by one's language. Vulcans may be logical enough to comprehend that, paradoxically, a too logical language could curtail their ability to keep up with the vigorous, passionate expressive power of their fellow races. As such, retaining mastery of their ancestors' less structured mode of speech and thinking, while of course raising a sardonic eyebrow at the quirks of said language, may keep the Vulcans on their toes...
Mathematics is a very logical langage and the Vulcans speak it all the time.
It is perfectly logical to retain the ability to communicate on a more primitive level.
As there is no accepted answer for this question, if I might chime in on a few points:
While Klingon has received a lot of attention onscreen and off for being an extremely robust constructed language, the majority of other Trek alien languages didn't get this treatment. QED - typically when you see and hear a Vulcan speaking in Star Trek the language is depicted as an alternative lip-reading pronunciation for their actual English lines. IMHO it's very easy to see this in Wrath of Khan while Saavik and Spock have a brief exchange in Vulcan.
Vulcans tend to be attached to tradition at the cost of logic, such that their past may not be easily forgotten. The enforcement of protection of rituals through brutal spears and halberds, for example, stands in stark contrast to their logical practices. One would expect that it would be enough for a typical Vulcan to be simply rebuked by a guard and reminded of the legal ramifications of doing so, and the would-be trespasser would acknowledge this and move on (or make a case for violating the law, plainly and logically -- the logical equivalent of talking one's way out of a traffic violation because your wife is in labor in the passenger seat). Hence, the language they speak (whatever the fine points truly are) may well be a holdover from those ancient times; no doubt subject to the same fluidity and adaptability as our own real languages, but still rooted in tradition. Put another way: archaic Vulcan is archaic.
Note that the 'most official' reference point for all things Trek canon on the web, Memory Alpha, has no mention of an official Vulcan language reference outside of the 'bad lip reading' practices seen to date, though it does acknowledge the actual spoken phrases as Vulcan and the occasional isolated words such as pon-farr, kroykah, and so on.
Ultimately, the answer to your question is most likely the fact that Klingon got the lion's share of the constructed language attention, to the detriment of others. In simpler language - they just haven't gotten around to it yet.
It would limit his conversational options too much.
Also, given the prevalence of Universal Translators, who says he isn't?
Why?
Script writers have too hard of a time trying to imagine themselves in the skin of a logical being, much less in the skin of their math teacher, or an autistic person with an unemotional affect and a logical bent. So they don't even try.
Pulp fiction isn't ordinarily written by specialists in linguistics, science or recreational linguistics pursuits such as creating fake languages. And that is good, it makes for good stories, but it makes for clumsy linguistics & clumsy fake linguistics.
Everyone has heard of Tolkien and High School French. If pressed to create a language, or imagine one, they will think of those experiences first.
Virtually no one has heard of Loglan, Lojban, constructed languages that do attempt to be logical and use logic as the foundation for grammar.
The grammar of loglans invented to date are mind bogglingly difficult to use, so script writers wouldn't likely be able to invest the time to plausibly use a loglan.
"Is canon too well established for future writers to fix this logical gap in the description of the Star Trek universe?"
Nope.
Allow me to elaborate.
Non-American citizens of Earth are notoriously multilingual. It is all but guaranteed that Vulcans know many languages, and use them as they see fit.
Vulcans are also fully capable of appearing to be illogical in cases where logic dictates.
In Star Trek II: The Wrath of Khan, Spock participates in a lie (which he calls an exaggeration when another Vulcan is confounded), by using days instead of hours, hours instead of days.
Because of this we can conclude that not only are Vulcans capable of altering their language, but they can do so in many ways.
In much the same way that Spock altered his speech while he and the captain knew they were being surveilled, Spock also refused to speak some of the more logical languages of Vulcan because there was always the chance that, while on a Starfleet vessel, the conversation was being monitored.
It could easily be concluded that it would be disrespectful, or possibly even dangerous, to speak completely logical languages around non-logical beings.
And much in the same way that the award-winning Doctor Who episode "Blink" treated its audience (the creatures cannot move while anyone can see them, including you, the viewer) this movie treats its audience as that of a group of non-logical beings, thus making you feel ever so slightly more "in-the-world." If we were to witness Vulcans using a language that they do not use around humans, this immersion would be broken, and the creator of the episode or movie would have committed an error.
And that's just not logical.
