I'm getting rid of my C6 with 57k miles on it this saturday. Bought it with low 30's on it. Still runs as good as new. As long as you keep up on the maintenance and don't beat the hell out of the car, it'll last a long time. If you are planning on keeping the car for a long time and don't care about it losing a ton of value, then there is nothing wrong with buying a high mileage car. If you plan on selling it in a few years, avoid the higher mileage ones. No dealer will give you anything reasonable for a trade in, because they only want low mileage garage queen cars, and private party people will lowball you "because of the mileage". I was considering trading mine in and the one dealer said he could probably give me around 17k for it. Its a 2008 black Z51, 3LT, NPP (the bi-mode exhaust) with 2 roofs with no damage/issues/etc. The other one wouldn't make an offer because he knew Id refuse it.
Also, one of the vendor sponsors on corvetteforum had a c6 that was closing in on 200k miles a while back. They drove it all around the country to all the shows and treated it as a demo car for some of their products. I remember reading the thread and since they properly maintained it, it ran like it had 20k miles on it.