Now I remembered what I wanted to ask.
Who's worth leveling? Are people going to keep popping in and out of my party? I assume I'll have Reimu and Keine, and probably Marisa and Nitori, for pretty much the entire game. But do I want to sink valuable points into, say, Rumia, or Youmu?
What Trickster-kun said, Daiyousei is definitely worth putting one level in to get the free heals. She will automatically level very fast once
she heals. If you go Reimu's route, I guess leveling Keine and Reimu is good, since you'll be using them the whole game. Of course, if you
take Marisa's route, level up Nitori and Marisa.
As for which characters I think are good. Keine is really good, her defense is amazing, so buffing her and giving her defense support is
exceptionally useful. Youmu is probably one of the best characters in the game, having solid defense, really high evasion, hit rate, and damage.
I like the 140 graze point buffs, the ones that give +10 to 2 stats when your power reaches 130+, those are useful.
Keine's wife ability, I find to be only so so. The xp bonus isn't that important, because xp scales in this game. Level difference between
you and the target gives you more or less xp. So, a level 10 Daiyousei uses her heal ability on a level 16 Reimu, she will probably get enough
xp to level up once. This is also why Daiyousei is one of the highest level characters in my party, but even so she will still get one shotted
if a boss hits her.
Remember, if you fly, you use up 1 MP per step. If you walk, you do not use up MP per step, and you auto-regenerate a bit of MP per turn.