Currently you are releasing two, Light Party, Dungeons. While good for fast, easy play I think it also limits you on what you can do in design. With a Full Party you have more access to mix it up since you have two tanks, two healers, and 4 dps. You can split the groups up, use crowd control mechanics in boss fights, or even have players control things like cannons and traps while other have to fight.
I know this would make for more difficult content but it's that the point? You would have a Light party dungeon with low ilvl requirement for people to gear up and a Full party dungeon for people to work on getting the best, mid core, gear of the patch.
As for roulette, LV60 can be Light Party and Expert can be Full Party.