Hmm, I sort of sympathize with the non-DF users more, because they truly have to work to succeed. I mean, Luffy is always coming up with new moves and new ways of using his DF powers, but that's pretty much it, he relies on his DF too much, as do most ability users. Whereas Zoro, for example, is always working out and deepening his understanding of swordsmanship (re: breath of all things) and still manages to beat DF users, who take their power for granted. I wouldn't like to see any of the "normal" Strawhats eat a Devil Fruit, at the moment.
You also have to consider that you don't always get stronger, didn't Lucci say there was a 10% risk of getting stuck with a useless power and unable to swim?
Apart from, that (not wanting to start an argument) Nami is not necessarily weak anymore, at least not weaker than, say, Chopper, a DF user (sorry, Chopper fans). Her fighting strategy just differs from the others in that, like Ussop, her specialty are ranged and elemental attacks (Nami is basically an RPG mage now) rather than taking on melee. It would also be wrong for Ussop to say that a Devil Fruit must automatically be stronger than any weapon he can construct.
So I'm saying either sell it or keep it for an emergency, perhaps even use it to kill another DF user by feeding it to him. xP