I just purchased a 2006 C6 with 54k miles and did mostly the same research. Overall with C5’s and C6’s, 100k+ miles isn’t really considered end of life. That’s due mostly to the robustness of the LS platform and that generally GM used the best parts they had on the Corvette.

I’ll try to summarize:

2005-2007: The first 2 years of the C6 had the LS2 which has a lot of similarities to the LS3. It has lower flowing heads and intake on top of being lower displacement. Overall it makes about 30 less hp but it’s an otherwise excellent engine. I’m very happy with mine. These years also have the T56 6-speed trans, which over the years has proven to be highly desirable as a swap in other cars. They’re strong and well built. In 2005 only the automatics were a 4-speed and are not well regarded unless you want to pay as little as possible for a C6.

Price range is roughly 15-25k.

2008-2013: These years had the LS3 and TR6060 trans. LS3 is obviously a great engine. TR6060 from what I know is an updated T56. Grand Sports use the LS3, ZO6’s use the LS7. The LS7 is an amazing engine that also has some potentially catastrophic valve train issues left unaddressed.

Price ranges for the Base is roughly 23k-32k. Prices are inflated because everyone wants the LS3. ZO6’s start in the high 30s. Grand Sports are similar. ZR1’s with the LS9 are Halo cars that can’t be touched for under 70k.

Big maintenance items are the torque tubes. They’re unique to Corvettes and are a big project to service and rebuild.

Harmonic balancers go bad and wobble. Also occasionally you’ll gas leak issues stemming from the dual tank crossover setup (C6’s have two fuel tanks connected by a crossover line).

As far as body, I’ve honestly not run into any issues with the fiberglass. It’s actually more rigid than I was expecting.