Yeah, if they were adding more content to the port, it seems to me like they would have advertised that it was expandable or would have DLC. That seems more appealing than just a straight port with altered controls, after all.
If they put it on the Vita, it would be incentive for me to run out and buy one despite there being literally nothing else I'm interested in right now. :P But I agree, I'd love to see a new game if it's not going to be another iOS thing. I might buy a Vita for one game but I don't see myself buying an iPad for it. <_< I can't imagine they'd go last-gen, though. Not when Square-Enix has released a fair few gems for 3DS already and is likely aiming to break into the Vita market with more than just ports. It's probably easier to develop for 3DS not just because they've already created several games with different studios on the system but because it's so close to the DS so they wouldn't really have to tweak all that much gameplay/design-wise from the first game unless they purposely wanted to.