Why is warp speed and first contact seemingly the most important thing in the Star Trek universe for a civilisation to become "enlightened" and then utopic?
For example, why couldn't the Prime Directive specify parameters where first contact can be made if the civilisation was close enough to warp speed, etc. For example, many civilisations may have travel within their solar system, have colonised a nearby solar system or several through sublight colony ships over time. The Prime Directive might still deem them "less technologically evolved", not ready for contact, etc.
Additionally, we now know that while mastering energy and matter is clearly a hallmark of a technologically advanced society, there can be other advances that a civilisation achieves before that - in fact, for example, manipulating the biosphere and genome could be attained before warp speed and may be a better test of whether they could behave themselves.
There are clearly civilisations which are benevolent and malevolent regardless of their attainment of warp speed. Yet, from the Federation perspective anyway, contact and technology transfer is strictly regulated, though quite confusing, eg. http://memory-alpha.wikia.com/wiki/Prime_Directive
Strangely, it appears that if a civilisation was part of the Federation, and/or had enough ties with the Federation (which ostensibly MUST have involved warp speed and first contact initiated by the "new" civilisation) ...then that civilisation is deemed to be "acceptable for co-operation", if you get my drift.
Update1: Thanks, the best answers thus far appear to lean towards a RISK VS REWARD situation. IF they have warp technology, well, you have no choice but deal with them, whether they are good, bad or ugly. Clearly warp travel itself is not a moral measure (and as some pointed out the Klingon situation seems quite complex). If they don't have warp technology, they may be 'good' (eg. 'responsible' genetic modification, constructive terraforming of their moon, etc) - but why gamble with giving them warp drive (likely from first contact) - since then whatever happens, the whole galactic quadrant will have to deal with them, for better or worse.
Update2: As for "guiding" a civilisation once they do achieve warp travel, that's still a controversial area (in-universe and to viewers) as per ST: Enterprise, etc. The ST Reboot Movies also touch on this, interestingly - why were they allowed to prevent a Volcano erupting? That seems like massive interference with a civlisation compared to allowing "primitives" to see a flying metal object... but that's probably another question in and of itself.