YAY! Once Piece!
*cough* Excuse me. I love One Piece.
I agree with Jerseymilk about Zoro being more like Piccolo than Vegeta. In my eyes both Zoro and Piccolo actually cared about their friends, a trait Vegeta lacks (Piccolo wanting to stop Gohan from fighting Cell, Zoro wanting to dive in to save Luffy despite the fact he had just had a tough fight and was still suffering from the wound Mihawk gave him).
As for Sanji as Vegeta, well, when I think of Sanji, the first thing that comes to my mind is the fact he's a skirt chaser, so I view him more as a young version of Roshi. Granted I never really considered Sanji having some Vegeta elements in his character. Perhaps Sanji would be best described as a fusion of a younger version of Roshi and Vegeta.
On the "fusion" idea, there times when I'd view Luffy as possibly having elements from both Goku and Gohan. In my eyes Luffy has a similar IQ level as Goku both in and out of battle, the limited interest in training that Gohan had (only do enough then get on with life), the desire for food that they both share. As for battle I might go so far as to sway slightly more towards Gohan than Goku. While the strength for both Goku and Gohan was driven by their desire to save their friends, I do feel it was something Gohan "relied" more on than Goku. After all, it was this reason that Gohan first transformed into a Super Saiyan. On a similar note, often Luffy displays the tendency to want to protect his friends. Take the Arlong arc for example. Luffy was driven to fight and beat Arlong after witnessing Nami stab herself in her arm due to the way Arlong betrayed her (Luffy never actually learnt Nami’s past). And at the end f the fight, Luffy gained a boost when he landed in Nami's room at Arlong Park and could see and sense the amount of pain she must have suffered in that room. Course the “jury is still out” on that one.
On an interesting side note, you could also view Shanks as being Goku like (willing to sacrifice something for another - Goku sacrificed his life twice and Shanks sacrificed his left arm). Also Luffy looks up to Shanks, perhaps even as a possible father like figure and/or those two having a father/son like relationship (that’s how I view it anyway). And Gohan always looked up to his father. Also Mihawk could be considered to be like late DBZ Vegeta. Why those two? Well...
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Shanks and Mihawk are friendly rivals as back when Shanks used to have his left arm, he could match Mihawk in battle (or something along those lines. I haven't actually read the chapter this is revealed in, only the fact those two were rivals).
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Course, that’s just my opinion.