If they are the same, yes. But if they are something completely different from the parks, and I mean more than just different rides - different park concepts, then I don't think it would be a major drain. I think it would capture a lot of people who otherwise would not make the trip to Florida or California anyway.
Animal Kingdom unfortunately didn't have enough of a draw on it's own, and people just couldn't extend their vacations anymore. That's where it went wrong. But I think in some ways it did help - I think that some people who would normally have taken one day out of Disney to head over to Tampa ended up staying at Disney that extra day.
I don't think there is going to be a whole lot of growth in the Florida parks for a while. In their ROI mindset it just isn't justified. They have to try something new, and I think they are worried that Six Flags is drawing away from their market share.