That's actually an interesting question, as we'd normally be so focused on what the 'lee is wearing. Personally, I'm a sock fan, so especially if it's a female going after me, a cute set does have somewhat of a "weakening" effect on me.
Bare feet for a tickler can also create a psychological effect, especially in combination with bondage; knowledge that the tickler's feet are as bare as yours can be both taunting and err..."helplessifying," in that you know that as exposed as those feet are, it's yours that are about to be attacked!