2000-2002 MR2 Spyders were prone to failure of the pre-catalytic converters, which can cause destruction of the engine. Fortunately these can be replaced. Pre-cats can fail a few thousand miles or a hundred thousand miles. Some can last hundreds of thousands of miles without problems. Pre-cats are a big issue but if you take the time to check prior to purchase and make a point of getting rid of them asap it's no reason at all to avoid any particular year.
To check to see if they are in good condition take off the two O2 sensors on the manifold. You can identify the O2 sensors by finding the two wires coming off the exhaust manifold -- the sensors are right there. After the sensors are removed (using a special socket) use a flashlight to see inside the hole. If you see a perfect honeycomb material you are good. If there is any deformation or bits missing that means you have a problem.