Owning a Z4, you know what having a fun car means. It means everything else you drive isn't as much fun.
There's no law against having more than one "fun" car that I know of, so by all means, go for it. You can't get more car for less money.
Just so ya know, I have three other pretty fair "sports cars" that I haven't driven since I purchased my Crossfire nearly 4 years ago.
With 40k miles on my Crossfire, I haven't had one "mechanical" problem that's kept me off the road.