Well, he could have, for starters, not drawn Franky into the picture if he didn't want to associate him with the Mugiwara.
And well Paulie just doesn't bring anything new to the crew… he looks like a younger Smoker; he's blond, (using the hair color argument) like Sanji; he smokes, like Sanji; he has a weird reaction to beautiful women, the opposite of Sanji; he has issues with money, the opposite of Nami; he's serious at about the same level as Zoro; I couldn't see him interacting well with the more goofy members of the crew, like Chopper; neither would he have much to talk about with Robin, unless he tried to steal her role as big sister...
Having Paulie in the crew would probably get us forever stranded in the same comic reactions to women and money, which other characters already cover quite nicely. We'd also see him trying desperately to look as kickass as Zoro and Sanji and, while his fighting style is very cool, there's just nothing refreshing to his take on fights on an emotional level. We need someone who's a lot more special than Paulie, and we certainly don't have anyone in the crew yet who finds a tense situation the perfect moment to strike absurd poses (re: Franky).
Franky just offers a lot more possibilities than Paulie, both on the fighting level, him being a cyborg and all, and on the interaction level. He could get on with all of the crew members, he fits in with them and he has quirks which are truly his own, like the poses, the guitar or the dependance on cola.
Paulie just can't keep up with that, although this is just my opinion.
Anyway, I'm already looking forward to the next possible character. A bard, right? Any chance we'll get another female Strawhat?