You really faster saves vs spell at 3 vs 1 of the other saves ?
I consider them at 2 vs other saves.
I put mal > Mental > Svs > aff.
I normaly aim to get at least 45 to 50 Mal (with Svs), and 25 pure mental saves.
Aff saves i consider less important, and can cope with the protection of vs Spell and the odd save from random armor piece.
The reason for this is that:
Mal saves normaly block the death spells:
Curse, Blasphemy, Blind, Plague, Poison, Enfeeblement.
This can have a huge impact if landed.
Mental saves normaly protect me from:
Dispel (that can be fleed and recast), and Sermon.
All others i can normaly avoid.
Aff saves, i realy dont care, because:
Invokers will eat your saves, or blow them up.
I can normally roll with the % associated with the saving of a aff spell.
IF the pain if to strong i just flee sooner.
Santuray + Protection already cuts these enuff.