Totally 100% agree with you there.
I think nakedness is so prevalent in tickling media because many consumers of such material equate it with pornography. In effect it IS their pornography and in my opinion it really degrades the entire experience.
As for real life tickling, for me anyway, nudity is just as uneeded. As a 'lee I think it brings sexual aspect to it which is great if you're with your sig. other and are engaging in what amounts to foreplay. But otherwise it would detract from the main purpose of the event (assuming it's a planned "event" and not spontaneous otherwse why would you have gotten naked?).
As a 'ler I agree for much the same reasons you listed. Not only is it more fun to sneak under the shirt of a sqirming 'lee, but it is also more effecting for him or her because the clothing gives them a very false sense of security. Thus making the tickling more of a surprise.
ALSO when naked, unless you are GLUED to the bed or wherever you are, you are just too free to get away, even if the effect is only psychological it's effective. There's nothing that makes you feel more trapped than something that is INSIDE your very clothes.
I'll use this situation which was described to me by a friend...imagine how effective it is when someone is tickling your thigh...and then imagine that hand being pressed and held there by the tough denim of your shorts. No matter how much you squirm around there is very little that can be done.
So anyway...my not so short or to the point answer.