I still only have 3 songs, and haven't even unlocked the 4th drum yet, but I am able to upgrade patapons now, and all the loot i'm collecting is no longer useless.... lol..
Although I'm eager to see when / how to upgrade weapons. I'm guessing more and more will unlock as I go. It looks like the developers force quite a long training/intro mode. Seems that's the rage the last decade lol.
I think after being a gamer for 25 years, I get impatient since ... you know. I've actually held a controller once or twice before :D