On Live this spell is seldom cast by players as Mass Suggestion usually lasts longer and has a higher impact as it can charm multiple targets. Being a level 9 spell, you'd hope it would be solid at endgame, but in Epics, even with a 42 DC, I've never been able to get this spell to stick long enough to be worth casting; not even on mobs like eVON1 ogres that have a Will save around 20.
In short, this spell (and its level 5 cousin) need some of the buffs that other weak spells are scheduled to receive in update 9.
I suggest the following:
Non-epic trash mobs:
If you are successful in overcoming SR and the monster's initial save, the monster is dominated for a minimum period of 90 seconds. While dominated it fights for you, and follows you throughout the dungeon.
After the 90 seconds expires, the monster gets a new Will save to shake off the spell every 12 seconds.
Non-epic orange named mobs:
These monsters are more resistant to domination. The guaranteed domination period is reduced to 45 seconds. In addition, each time the miniboss fails a Will save against the Dominate effect, it gets a stacking +2 to all future saves against that effect.
Epic trash:
As non-epic orange named mobs.
Epic orange nameds:
Bending or breaking the will of these powerful foes is not easy. These foes have an inherent +10 to Will saves against all Domination effects. Otherwise, they are affected in the same way as epic trash.
Red/Purple nameds:
These, of course, retain their blanket immunity to all charm and domination effects.
I think these changes (or something similar) would make the Dominate Monster spell worth at least considering giving up one of Mass Hold, Energy Drain, Power Word Kill or Wail of the Banshee to take.