Was Dumbledore aware of house-elf magic? If he was aware of house-elf Apparition, he should have gone to the Cave with Dobby. It seems nobody in the story made use of elf Apparition fully (it isn't abuse, as making use of Hermione's magic wasn't abuse).
For instance, Harry might have gone to Hogwarts/Gringotts in the final book with Dobby/Kreacher (along with Hermione,Ron) avoiding much trouble.
What are the limits of house-elf apparition?
This probably doesn't answer your question, but I would like to point out a flaw in your reasoning:
It seems nobody in the story made use of elf Apparition fully.
The characters you suggest would benefit from elf magic would not make use of elf magic. They didn't use elf magic because they viewed elves as individuals deserving of respect. Had Dobby survived, Harry certainly would not have agreed to his going to Gringotts just to provide an easy escape. Harry cared for Dobby and would not want to put him in danger.
Voldemort provides an excellent counter example. At the cave Voldemort requires that Regulus provide a house elf for use when he goes into the cave. Voldemort uses Kreacher to drink the poison and then leaves him for dead in the cave.
