Don't get me wrong I think air on a new school car that's worth lots of money has it's place, it's actually quite a sensible practical idea. Car can go low, but raise it to prevent damage or to drive harder on poor roads for instance. But spending 2.5k on suspension on an old mk2? Only if you tell me you are going all out show car and are going to win trophies, and have paint, interior etc to match.
Otherwise spend your money more wisely.