Wheelies can't be any worse than a full on wreck, and a lot of amatuer races (myself included) will ride the same bike after its been wrecked many times.
As far as fork seals go, yes you'll blow them out, especially if you haven't adjusted the suspension properly to compensate for the stress of stunting. But fork seals are cheap, and rebuilding forks isn't that big of a deal and should be done every year anyway.
As for me, the only wheelies I pull are on the start of straight and under hard acceleration.
