Gents, if I could employ your assistance with some questions I would appreciate it. Personally I am the owner of an E36 M3 but a good friend of mine longs after an E30 M3. He has found a fine example but had a couple of questions I could not answer. This car he is looking at is essentially a race ready M3, highly modded.
1. Would the value of the car over time decrease more than a stock or near stock M3 because it is so highly modded?
2. Is there anyone near Carlsbad (North County San Diego) in SoCal that has a stock or near stock M3 that he could call to discuss the finer points of E30 M3s with and possibly take a look at theirs for comparison?
Thanks for any help on this.

A truly "Race Ready" E30 M3 will not depreciate much. However it is very expensive to keep an E30 in "Race Ready" condition.

A stock E30 M3 that is just racking up miles and problems will depreciate, but I dont see them EVER dropping below $4500 in driving condition

A low mileage, totally original M3 will retain its value very very well.