We had a 2.0 Mk3 ‘Sport’ model for about 5 years from new. Previous car was a first gen BMW Mini Cooper S Works, and compared to this the MX5 felt very dull and pedestrian – although much more comfortable, and with effective brakes! Having driven a Mk2.5, I felt the Mk3 was pretty cr*p. Main reason the Mrs and I went for the Mk3 is because we’re both over 5’10”, and in the Mk1 & 2’s we tried, it felt like I was in a kiddie car – head poking out of the roof job.
However, after chatting to people in the local MX5 owners club, I bought some Eibach springs and anti-roll bars for our Mk3 and took it to a suspension specialist – this completely transformed the car, and basically it felt very similar the Mk2.5. If you do get a Mk3 that hasn’t been lowered, I’d strongly recommend you have the suspension upgraded; FWIR, it cost about £600 including the proper set-up. The latter is well worth getting an MX5 specialist to do. We had a ‘fast road’ type set-up and it was mint – loads of controllable grip, cornered really flat, but was also still a much more comfortable and less jittery than the MCS Works.
The only other thing I can think of at the mo., is that, again FWIR, the Mk1 and 2’s engines are easier to tune than the Mk3’s (2.0 anyway). The 2.0 engine is a bit of a characterless lump, but there may be some more tuning options available now – I think someone was developing a supercharger kit for the Mk3 1.8 engine:)
Anyway, I think what I’m saying is, if you find that you can get comfy in Mk2.5, I’d get a good late example of one of them rather than a Mk3.
HTH and good luck.