Hopefully you may have noticed that the older Mr2's suffer from a lot of surface rust on the suspension parts etc... Lee has had all of those parts recoated. When I was looking for a donor, there seemed to be a definite point in the mr2 mk3 generation that Toyota changed their protection coatings of these parts and the facelift models still look good under the skin.
I have an early model but it was exactly what I wanted- untouched and original with no damage and only 60,000miles, but the panels had trolley damage. It was also very cheap because of the knackered engine.
Don't buy a 'cat' rated car, future buyers will always wonder what the kit is hiding
Buy the best you can afford, age is not the most important, low mileage will reap benefits. Also look at the parts you'll be keeping, namely the underside of the body.
The Ferrari's are black under the trunk and bonnet, so a black donor is a step forward, these thing help with the build as it progresses.
If you are looking at an engine conversion have a look out for the ceramic damaged engines, these are cheap and save money on something you'll end up throwing away.
D