You better grab E30 M3s while they are 15k-20k. I'd imagine that any M3 coupe / convertible will shoot through the roof now that present M3s are sedans. One sold for 19k last year here in st. Louis. First time i seen one in the flesh and it's truly a sight behold.
Z8 have always been increasing as well.
E30 M3's under $20k ended a long time ago. Unless it's a salvage title or a dog (200k+ miles), it's not happening. Average values are already around the $23-28k mark. $30k+ isn't unheard of at the moment.
Had 115k miles. I didn't see 8- Series mentioned at first. A local BMW Specialty dealer is selling the V12 model for 20k as well with 60k that i had my eye on as well as a V8 for 10k. Wouldn't doubt those not rising either. We have a ton of great deals on cars. Everything is dirt cheap!