| I haven't been tracking prices on our cars lately because my effort to automate my CL queries stalled out, and the demand from work ramped up to the point of overload. I consider 6.9's to be fairly predictable, and fairly low. 6.3's are even less predictable than ours, imo, as I've seen great cars go for ~$30k, and rotted out hulks go for $20k. 600's remain stratospheric, and rare enough that the people paying for them these days don't likely care what the car costs.
Twice in my life, I've almost taken a gamble on a car that I wanted, and could've bought it and later re-sold for a significant profit.
Outside of those two cars (neither of which I actually bought), I've lost money on every car I've ever owned. If you have money to spare, you'd be far better (and safer, in my unqualified opinion) to invest it in a stock portfolio or something else than spending 10+ years sitting on an old car and hoping that it turns a strong profit. Now, if you buy a car you love, and sell for a profit down the road? Then it's probably worth the effort, but unless you're willing to risk a 100% loss, buying cars as an investment is probably a bad call.
NOTE: I'm not a financial advisor, I do a **** job of taking care of the tiny amount of funds I have, and probably shouldn't be listened to.
1976 450SE 6.9