I find him and the chivalry he embodies completely impeding to Nami's development. I would like to see her do things, fight, take her share of hits and get just as dirty and messy as the guys, thank you.
I agree with that, I'd love to see it happen. But it won't because apparently in shounen girls aren't allowed to take real damage or whatever because it is inherently a bit sexist as a genre.
But in all fairness, Sanji really doesn't do THAT much for her. A lot of what he does is stuff she asks him to because it either needs to be done and nobody else is reliable enough to do it (see: shoveling snow off the deck of the Merry) or he needs to stop fighting with Zoro over something stupid (Davyback Fight, asking him to steer while they're escaping Enies Lobby). I don't ever remember him offering to fight anyone for her, nor him freaking out about the idea of her going to fight someone on her own.