I have followed one simple rule to keep me out of financial trouble with toys/hobbies. If you can't buy 2 of them with cash, don't buy 1 of them. That's obviously on the buy side. On the selling side, if you have something that has strong value, say 50-60k it may make sense to move off of it. You can buy nicely appointed cars in the 20-25k range, allowing you to pocket 40k. Had this been done a year ago, your 40k would be close to 50k right now. As long as you're realistic about your situation and what your car ACTUALLY costs you, only you can decide what is right. People rarely know true cost of ownership. From maintenance, time, insurance, etc.
Be honest what about your car is worth as well. Countless times people hang on to a belief their car is worth X, only to find it's X - 20%.
If I used that philosophy, I likely wouldn't buy anything. Which may not be such a bad thing, I guess.
On the selling side, my car is probably still worth what I paid for it 4 years ago, possibly even less since it left its cushy Georgia climate and has been stuck in the winter hell that is Ohio for three winters now. I don't have an overly high opinion of what it's worth, but man, if it was done... A triple black N-96 4-speed console/buckets has to be at or near the top of the 383 food chain. I can't think of a way it would be optioned better.(other than having a stripe, disc brakes, a 26" radiator and 3.91 gears)