Great cars. We had an early Jap 1.6 and it was bombproof, and I’d have another in a heartbeat.
Not sure about a) trouble insuring imports, or b) avoiding modifications.
a) the majority of my cars have been imports and I’ve never had a single issue getting insurance. They’re no more expensive to insure either.
b) if you get one that’s been modified properly and sensibly you can end up with a much better car. Things like lighter wheels, better tyres, sports springs/coilovers, brakes, exhaust & induction can all lead to a more involving drive.
An alternative, with more oomph but just as reliable, would be a mk2 MR2. Maybe bit chavvy and their reputation for a snappy rear end isn’t unfounded, but they’re roughly the same pricepoint as the MX5 and are really excellent cars. No soft top but the t-bars are almost as good.