For me personally if I could change anything in the roulette it would factor player levels a bit more.

Getting basic Sastasha for example when the lowest guy in the group is 50+ Would be nice if the dungeon was a little more appropriate to the lowest person in the group.

As for mini trials. I've found the bonuses from them seem to be in line with the bonuses from equivalent dungeons. The bonus from iftit story is about the same as the bonus from halitali or toto rak I think.