I think the only reason Wobbuffet was banned in gen 3 competitions was because if two of them were ever sent out in single battles the game may as well have frozen, what with no direct method of attack and the only possible ability being one that prevented switch-outs. As for whether or not it's worth training one, that depends entirely on how good you are at out predicting your opponent. It's not really worth it in-game, since trying to out predict a computer opponent is usually an exercise in futility.