A couple Questions

[Niwashi]

I have done each instance only once (I know this can use some improvement).

Do the Duty Roulette. It gives you a random dungeon from among the ones you've already done (well, not entirely random, as it's usually whichever dungeon someone else specifically queued for, so that you can help fill in the rest of their group), and not only do you get the high level of mob-kill XP that all the dungeons have, but once a day you get an extra XP (and GC Seal) bonus at the end. (Well, sometimes it can put you in a primal Trial instead of a full dungeon. In that case, you don't get much mob-kill XP, but you still get the completion bonus, so still worthwhile.)