The trick with targeting weaknesses, I think, is having them be ones that the character needs to avoid and let another party member handle rather than just relentlessly smacking the character with something they can't handle. Make the players think strategically to have the character with high saves or controlling abilities keep the enemy controller/debuffer busy so the one with low saves doesn't get wrecked. It's the same principle as having the tank keep enemies away from the support.
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On getting through spell resistance, the first level spell Sure Casting gives you a +5 bonus to get through SR on the next spell you cast. My sorcerer has it as a Known Spell, but a wand of it would be cheap.
There's also dweomer's essence, from the Pathfinder Society Field Guide. ^_^
500 gp a shot, but much better for action economy (it's part of casting the spell rather than a separate action).