I've had a supercharged Z4 3.0 and a Z4M, as a fun daily car both the E85's were great.
I sold my S2000 to buy the Z4M, which I'd run for 2.5 years. I then had the opportunity to buy my old S2000 back and I jumped at it, think that says everything. It was more engaging and a more fun to drive the Z4M, but only on the right roads (i.e. quiet and up in the hills) and as a weekend car it's sublime. Whereas the Z4M always left me feeling disappointed, even with some tweaks, despite a great engine.
Really depends what you want from a car. I've had 24 cars now and the S2000 is the one I've owned for the longest, must be 5 years in total.
Really no idea what to replace it with without having to spend silly money. Back on here looking at the G29, but not sure that's going to cut it either, look forward to seeing it in real life.