In regards to price: I agree that $55 is mind-blowing. As a long time Tekken fan I already have beef with Namco, and seeing this latest App Store debacle didn't help.
HOWEVER, I kept my eye on the title and when it went down to half price I went ahead and got it. I am not sorry I did. In fact, I am quite happy with it. I figured I just spent $20 on Xcom (totally worth it) so what the hey. I got Melodic and it's great. The animation is great IMO and it looks sharp on my iPad and my phone.
I'm a Miku Flick fan as well and have both those titles. Those are great. This game has more content, however, and I don't think you can compare the two. The rythmn game is only part of the game; there's a bunch of other stuff to do as manager of your idols.
I still think Namco went overboard on the actual price (as compared to other games on the App Store) and I wouldn't have got it unless it was on sale, but now that I have it I have to give credit where credit is due. It's a high quality game and if you're into Japanese anime and/or game culture you'll probably really enjoy it. I played it for several hours last night and was having a blast.