I had a Mk3 2.0RS for 5 years as my only car.
I certainly am not missing the cramped cockpit, tiny boot, wind and road noise, harsh ride, unpredictable handling on the limit (largely due on mine to a combination of LSD and no traction control), pathetic fuel range, dubious build quality, crap bose sound system and useless local dealer.
On the plus side it would do 0-60 in 7.5s, the soft-top could be raised or lowered in less than 5s and dealer issues aside was quite reliable.
Given the choice now between a new MX5 or same money spent on a second-hand SLK, my money would go on the SLK. At less than 2 inches larger all round it is infinitely more comfortable and has more boot space even with the hard top down.