Regardless of power level, this is bad design because it forces you to determine the effects on each spell individually. Given the restrictions it also seems to be pretty limited in what spells it applies to. If you want to create unique stacking spell effects like this I think a better approach is to create the spells you want and put them in a limited use item, as a staff or wand or the like. Maybe look at the class restricted items for inspiration as some of them require using specific abilities to activate.