PKing
-Create minor preps, cures, etc, that is effective at that level range that becomes less effective the higher level you get to having no effect. This I think I would help encourage more battles, that aren't ended instantly by something like double thrust, or even bash.

-A few more weapons and armors that have minor effects (I know some of this has done) that can be obtained by this level range, but the gear itself wouldn't be as vaulable to a hero level.

Exploring
-Someone further down had a great idea. An area explore for mid level characters. I'm sure a RP reason to not allow too low or too high level characters could be designed. Also, not penalizing exp or reducing it in this type of area could be a great way to encourage it.

Quest
-More, fun automated quest are always enjoyable, especially when it tells more lore of the game, or provide tools that can be useful.

-Maybe run some mid level quest. Imm Interactive quests are always fun.

RPing
-More over all interaction, via yourself or as a mob. Arena contest, and all sorts of things.

Just some random thoughts