[Illuminated One]

I think not.
You can get a bit better stats out of it but not enough to place the mage at the frontline. And you loose all slots except two misc slots, so you are very limited when building something out of it.

However I think this spell is rather good for human mages:
If you have no intention or not the capability to really equip your mages it is a nice alternative to giving them shields or armor and some animal forms are probably an even better defense when someone casts earthquake or similar spells - additionally the enemy will not get hold of items when you loose.

Another point is that you most of the time get very good movement. Forrest Survival, Mountain Survival, sometimes even Flying or Stealth. Now your mapmove 1 mages can keep up with your armies, are upkeep-free, and not as easy to take down. I think that's really worth 3 nature gems.