SRT-6 springs can be had for less than $130 (or maybe free if you trade) if you want a *really* firm ride, but most people seem to find them a bit on the opposite end of harsh without aftermarket shocks.

Koni shocks aren't really cheap ($650) but they made a world of difference in the handling of my car, and they're pretty easy to install yourself (took me a few hours on a Sunday with 0 shop and 0 tools, just a driveway and a basic mechanic's set, although I am pretty handy with a wrench).

Mine was starting to feel a bit sloppy at 60k miles, and while the shocks that came out felt okay being compressed in a vise, I think they might have been getting a bit worn.

Once I fixed a few easy issues (hatch latch wrapped in electrical tape, windows adjusted), my interior is wonderful - it looks a bit chrome-y and less "expensive" than its Mercedes brother, but everything's tight and quiet, and everyone who gets in my car remarks about how nice it is inside. And my leather seats have 1 blemish on the driver's side bolster after 60k of wear - I think that's pretty darn good.

My shifter doesn't feel like "pudding" but I'll admit it's not the best shifting car I've ever had - people on MBWorld say that a better transmission fluid (Royal Purple, Red Line, or the like) helps the shift feel a lot for a few hundred bucks tops.

I'd drive all the cars you're thinking about and see what you like best, but I'd keep in mind that for the price of a used Z or Mini S, you could buy a mid-miles Limited and put a few thousand dollars into making it handle, look, and feel great.