I bought my '91 c4 last January. It had been an "occasional use" weekend car, 2k miles per year. I bought it and made it my daily driver. I beat the pi$$ out of it every day. I drive it like I hate it, and I love it. 22k miles in *not quite* a year, and it performs flawlessly. The locking diffs (964 only) make it absolutely unstoppable in the snow. I can get through heavy snow that my chev 4x4 can deal with. No kidding
There's also another local guy with a 1990 c4... 270k miles on his. Engine's never been apart and the car works great.