TL;DR version: It depends.
If you're not able to consistently run 80 stam event maps or farm Mission 12 then it's not, in itself, a bad deal. Otherwise, you can get ampies occasionally on your own.
That said, if you're not able to run the previously mentioned stages, then you really aren't in a place where you should be looking at ampies anyways. Yes, the ampies will help, but not in any noticeable way when you're only adding one of each type to a girl (it takes 100 ampies of a given type to max the relevant stat for one girl).