Use for R'lyeh void summons ?

[Ctennyson]

My Last R'lyeh game, my Starspawn priest made it all the way to summoning level 19 before feeblemind. By that time, he had a chalice, too. He quickly got better, and went all the way to 25.

Priest has a %5 feeblemind chance. Mage, also called Starspawn, big diff, has a %20. Thats a big chance, and might be why you are feeling its so common.

Stargazer is practically immune.

And I also recommend the spell returning. At 2 astral gems every 8 turns or so, its practically free.