Also.. my opinion:
Chopper: Wing/Glide Point or since those birds rule of the people maybe they know of some kind of enlightened animist manifesto that will allow him to control monster point or something similar..
Robin: Secrets. Some kind of evolution of hana-hana maybe. Maybe being able to do many things at once if they force her to build and they find out her power.
Nami: Storm tier weather manipulation
Brooke: Now that I think of it.. the Longarm tribe may have prefected sound-as-weapon techniques and Apoo just has a musical instrument fruit and knows of these techs already. So he makes peace between them and that cult.
Ussop: Not sure. Training with Heracles. Maybe speed, armor or some new device for him to invent with.. like dials.
Franky: COUP DE BEAM!!! SUUUUPAA!
@threedayslater:
I don't think Sanji's greatest fear is Okamas. I think he's annoyed that they tried to/succeeded in putting him in a dress, but he's not afraid of them. And how exactly is cross-dressing going to help his resolve again?
Look at his face since he's gotten there. The only greater look of terror I've seen in an OP character is Ussop.
Maybe it'll allow him to empathize and have a greater understanding of everything. Yin and Yang. There's a masculine/feminine side to everything.
He's probably afraid to show that side of himself and now that's he's walked in a woman's shoes (or carried them at least) it'll make him a better person.. even if it's just towards woman.. he just swoons at them and he never gets what they're thinking and doesn't notice. If he understood his female side better.. and since females are the most important thing in the world to him.. it should make him a better person and be able to develop, be a more mature man and become stronger.