FWIW, I'd run a supercharged Miata (2nd gen), if you can live with the small trunk.
You'd have a light, balanced RWD chassis, with a useable powerband (plenty of torque down low). Having spent a fair bit of time in a 2001 model, I have yet to drive a 2-seater with more poise, precision, and balance.
The Mini Cooper Convertible strikes me as a poseur's convertible.
It's heavy and FWD only exacerbates the dynamic problems inherant to that kind of setup.
The Crossfire - aesthetic debates aside - is also pretty portly. Something to consider.
MR2 Spyder - Production is scheduled to end in June 2005. Compared to the market for the NB Miata, it will not have a lot of aftermarket performance support. Virtually no superchargers or turbochargers are available.
S2000- Another solid performer, but if you're interested in 'verts like the Crossfire, the hi-rev powerband may not suit you. :dunno:
Z4 - Even BMW's meticulous chassis and drivetrain engineering can't redeem this car IMHO. It's an aesthetic abomination IMO. And FWIW, you can build a smog-legal 2nd Miata that will absolutely conquer the Z4 - both in handling & power - for less.
The question I'd pose is: Are you looking for a pure-bred sports machine with fewer frills(Miata, MR2) , or are you more interested in the heavier "GT" convertibles like the Crossfire or 350Z Roadster?
My pitiful 1.9¥.
