18~30 hr (random) respawn rate will create more feeling in hunting imo

Harder (hardcore hard) NM possibly with special event-battle not just tank-spanking (based on NM's i watched on youtube)..

respawning minions might be fun

or free for all NM..loot goes to party with highest DPS?(8 man parties)..free for all NM = REALLY pain in the ass hard

Last, the loot must be an armor/weapon or some special equipae item and not just a material.. Boss drop should be > craft items