I had a '91 SC that went 112K on the original plugs AND wires and was only barely missing.
Just like ANY OTHER CAR there will be better built examples out there.
The Thunderbird SC is a great car, cooling and head gasket issues seem to be the only troubles. It isn't an easy engine to work on ( to get to the back plugs you have to go up under the car and feel for them ), but it can be rewarding, the SC can be turned into a quick vehicle.
95-95's had 230 HP from the factory, and are the rarest. If you find one in moonlight blue ( '95 ) and 5 speed, you have a pretty rare car.
MN12'S don't get the respect they deserve, remember that car was voted car of the year when it first came out, they called it the poor man's 6 series.