Low level spirit better as a mage in impossible?

[Leind]

I play mage in impossible. I'm level 12 with the spirits level 10/10/7 (so far haven't got Reaper).

The enemy stacks are so big that the damage skills are not very good, except a long Ice ball throw (fun skill. feel like playing bowling).

Now I use a lot more the crowd control skills (armor/wall/etc.) And since these one are good enough at lvl1 (getting 300HP or 100Hp for wall is the same as it will die in one hit anyway), is it a bad idea to level up spirit?

Because I don't want to end up with a wall that cost 30 rage.

As a mage I gain rage naturally very slowly in most of the fight (+1/+2 per attack and my own troops don't get hit very often).

Is it a good idea to make an extra effort to level up spirit? So far I have been doing that by using Inquisitors and potions and chargers (to chains fight without letting the rage drain).

But now I ask myself, isn't it better to keep spirit at low level to keep all the crowd control ability at low rage cost?