Unfortunately it's a bit of a waiting game when selling a Z3 which depends on finding someone who is in the market for one - no different to any other car really but I suspect the active population of buyers for a Z3 is much smaller than it is for most other cars. However, as we approach summer this population will always increase.
If I were you I'd definitely look at switching the side grills and selling the ///M variants separately.
In addition there is always a strong market for the OEM radio but I appreciate selling that separately is problematic if you don't have an appropriate substitute.
The final challenge is competing with other sellers for a buyers attention - but I would say that on the basis my 2.0 is also advertised for sale on the forum.
Joking aside though it's always worth looking at what else is out there and pricing yours accordingly or positioning it based on it's relative strengths / variances
GLWTS