I had decided I wouldn't grind before finishing the game, but... I've found a usefulness for the monster skirmishes in spite of that, I'm just taking my unused characters and playing through them to level them up´and make them close to my main party. This way, I can play through the skirmishes a bit and not overlevel. It'll also help me pair up the girls I'm not using in the main chapters...
I think it's interesting they've made some 'sub-missions' of sorts for the skirmishes - like when a merchant and a monster appear together, there's a rescue mission, and when a monster appears alongside a spotpass team, they'll fight alongside your team against the monsters.
Also, do legacy characters retain their original growths? I got Florina last night and I am wondering if I should pair her up with Sumia and form a flying death duo.
At the very least, DLC Marth's growths are signficantly better than his original ones, including a crazy 90% luck growth (+20% from good growths resulting in 110%). The actual growth rates of the legacy characters, DLC Marth aside, has never been officially revealed though, and it's impossible to hack 3DS games right now to find the growth rates, so, you can only go by personal experience.
I've started training my Florina though, and so far she hasn't gotten a single level up bellow 4 stats.
Also, completely pointless, but I've found out that spotpass characters have
one line after joining the party. Take them to a shinning tile, and if they find an item there, rather than experience, they'll say "What's this...?" rather than just the usual "...!" or "...!!!".