First of all, I apologize in advance for typos, I'm writing from my cell phone and I have an long history of lost fights against touchscreen devices.
Back in topic, I never liked the concept of spell adders because I feel they conflict with the spell point system. I mean, if an item gives me the power to cast two level 30 spells why it shouldn't allow me to cast sixty level one spells? The amount of power required is the same.
So I was thinking to remove tham and introduce a different kind of object to help mages. Multipliers are too powerful for my campaign, I'll allow a x2 at high level as a very powerful reward, and a x3 should be a relic of legend. At lower level a PP adder should do the trick, but it's very underpowered if compared to any adder.
What do you think about making Adders items that give you PP per day equal to your level? Maybe it would solve the "nonsense" problem.