I wonder the same. I have checked KBB many times over the last 6 months and the value(s) of my E92 m3 with mileage ranging from 17,XXX to 18,600 have been $43,000 to most recently approx. $42,000. I want the M4 and am on the list for one so I am not sure if I should sell now while I still can or wait until my M4 comes in so I can trade it in/sell it then.
And my car is a base M3 with just premium package and 6MT. Immaculate condition, too.
2008 (07/08) E92 M3 BPM Stage II Tuned by Mike Benvo, 6MT, Turner Test Pipes, Magnaflow Custom Catback Exhaust (Magnaflow X Pipe, secondary cat delete, Aero Resonators and Helmholtz Chambers),Vorsteiner CF Lip, Hamann Style CF rear diffuser, CF Rear Decklid Spoiler, BMW Performance Kidney Grills, CF Side Grills, OEM GTS Wheels, K&N Drop-In Filter, GP Thunder 8k Angel Eyes, Painted Reflectors.