just to add my tuppence in
my girfriends now on her second mk1 mx5. the 1st one was thoughfully set on fire by a local garage we asked to weld the sill for the MOT

as mentioned before structurally check the sills, check the sills ..... oh and while you're there check the sills

mecanically their pretty good, top end can be a wee bit rattly at start up but so long as that goes away quickly its ok ... another famous weak point is that they overheat. on both my girlfriends changing the rad fixed the problem, you can get new ones off ebay for less than £50 so not too dear ...
must admit I've driven both of them and like them a lot. I'd have one and I'm definately not a hairdresser

Brett