I agree with you about Persona 4. I mean, I would have been fine with another remake since I love P4 to death, but seeing as I beat it once on the PS2 and 3 times on the Vita, I dunno if I'd really be psyched about a third version of the same thing (Persona 3 did this as well, but that was a different case when you consider the factors). So I'm definitely glad it turned out to not be a remake (and even more glad that it turned out to be so much more).
As far as the Dance game goes...my jaw dropped. It dropped because of the paradigm shift...but I get it. Persona has always been proud of its music, and this became even more the case with Persona's 3 and 4. Not to mention that the Shin Megami Tensei series has been branching out its genres for years, with one of the newest branches being Persona 4 Arena (the original). And, as popular as the Dance Rhythm games have shown to be with games like Dance Central and, more relevant, Project Diva, it's not really hard to understand why this game exists. I'm down with the idea of it, and I might even buy it myself, being both a fan of Rhythm games and Shoji Meguro as I am. Though...I've never actually played Project Diva...but this seems fun enough.
I'm pretty psyched for the 3DS one, it seems pretty interesting. It doesn't look like it'll be any lighter in tone save for the appearances of the characters. Plus, this is the 3DS' first Persona title (of sorts), and I'm interested to see where it goes.
As for Arena...I'm still kicking myself over buying the original just before they announced the sequel. Still, I'm looking forward to it, since the original was incredibly polished and well done.
And, of course, I'm excited for Persona 5, even if they're only giving use incredibly small taste testers.