Can not sew, I have to politely disagree with your first two. Though I totally agree with the third!
I would say:
DO prepare as far ahead of time as possible. As many people have already said, a good presentation takes practice, practice and more practice. You can only do that if you plan in advance. It seems like the problem you had could have been solved with better communication. Also, a costume is not a waste just because it's not worn in a masquerade. Your effort on the skit may have been all for naught, but your effort on the costumes wasn't.
DO be original (and do take advantage of spellcheck) but DON'T do something "really weird" that has nothing to do with your costume/character. Whether you do a walk-on or a skit should depend on whether you can come up with a good idea for one or the other, not on the quality of your costume.