I'm sorta with purple5ive here, but really depending on the overall condition of the car. If almost everything is mint except the engine then maybe worth while to drop in a bare good condition motor. These cars are still pretty awesome as you mentioned.
Otherwise the GT86 is not a bad choice, even tho the old car has character, new car will always be, well...new lol. Much less to worry about just turn it on and drive. The GT86 is actually quite similar in a few ways.
But obviously is you really love your MR2 then $$$ no obstacle. Just my 2c :)

yeah the car is by no means mint. decent condition, sure. interior carpets were all replaced recently before I bought it (6 or 7 years ago?). seats are in good condition, no tears on sprung springs. gearbox recently rebuilt (last few years), new exhaust 5 or 6 years ago. the only non-engine issues are a bit of buffer work on a rear wheel arch, and one of the front wheel bearings is a little looser than I'd like, but not a worry.
 
I've ruled out engine rebuild now. just need to decide between engine swap and keep it, or sell as-is. also not going to do engine swap and sell.
 
argh, so painful to decide.