I cannot say enough great things about my 2005 M3 Competition Package. It is awesome in every way.
If your 3er coupe has been good, then extending the lease is not a bad idea, but I do not know what the increments are? Is it 1,2, 3 years, or do they allow 6 month increments?
Consider the E46 M3. It will be at least 1-1.5 years before we have the E90 M3 (and besides from the Amazing!! hp and torque of the new upcoming ///M...I think the E46 looks sooo much better). Lease an E46 M for 24 months..if you love it you can buy it, extend your lease..or get the E90. It's a win, win