This question was brought up recently by a player in our Pathfinder group who was planning to use the Permanency spell on the Resistance spell at later levels (applying the price for permanency and all of that) to simply upgrade the party's Fortitude, Will, and Reflex saves over and over again, effectively raising them all by an additional +1 each time. And, more to the point, that player wondered if you could continuously and repeatedly make this spell permanent on a single character or creature. Our group couldn't find anything in the spell rules for Permanency and Resistance.
We considered which spells might be stackable that we know are affected by Permanency, like Reduce Person or Enlarge Person spells; ultimately, we found that for those spells in particular say in their spell descriptions that they cannot be stacked, while the description(s) for Resistance (and of course, the Permanency spell itself) do not.
TL;DR, the question I have is as follows: Can a spell be made permanent on a character or creature more than once to stack the effects of that spell, provided the spell's description does not disallow stacking?
I'd prefer RAW answers, but any answer regarding rulings will do.