I'm running a Kitchen Sink Setting and magic and psionics are usually very hard to balance. One thing that makes it a BIT easier is Supernatural Transparency. I'm taking a rule from D20's Magic/Psionic Transparency but applying it to anything supernatural.
This is important when there are very different beliefs in the setting, beliefs that say the other belief should not work. So a Catholic ritual of warding works (probably derived from the cult of Mithras religious ritual and latin requirement maybe) as well as an South American's Rainforest people's method of Warding when stopping a "Catholic" Vampire or some South American ethnic monster.
Of course, supernatural is a funny in a game when you go back to real life. like Transubstantiation in light of a setting where all religions have some ability. lolz. I'm not in the game to argue religion but I'm the GM and I have to allow for these things.
So in this setting, a "Shady" minister can actually have supernatural powers while the holiest and devout monk may not have any depending if they have points and in the inconsistency of supernatural benefice. A obscure Cult leader can have more supernatural power and a greater connection to his god than a world renowned religious leader! (never underestimate the power of Marketing and Propaganda).
Information Asymmetry is going to be a constant, accepting it as a part of life and its challenges and "gaming the hell out of it" is a successful adaption IMO.
Wow, i just realized: does magic require cultural familiarity and language? If using an Ancient Egyptian spell, one must be familiar with the Culture AND the language enough to word it precisely? hmmm, if I'm going to use Ritual Magic (GURPS Magic p. 200)