Two full shifts of success translates into one extra damage shift instead on the usual 'one for one.' I've decided this also applies to enchanted items. This does not apply to Thaumaturgic rituals (but does apply to Evothaum).
You mean, every shift of power=1 shift of weapon damage. Not Shifts of success...
Thaumaturgy doesn't have weapon values on spells. Arguably, Evothaum doesn't have weapon value either.
Please let me know how capping the Lore works for you. We do it in our game and I haven't noticed much of a change, but I haven't spec'd my character out for maximum damage. IE, I haven't taken a lot of refinements and boosted control to an insane amount.
You should be wary of aspects to make sure they're not cheap. On the other hand, using up mental stress to create an aspect doesn't sound that powerful. What you should do is this: if it's fragile, tell them they need to tag it by their next turn, otherwise it dissipates. This prevents them from stacking piles of aspects and tagging them all at once. That said, it doesn't cost much more power to make it sticky, so I don't see how that will impact anything.
What kinds of aspects are they creating? Remember that 3 is a baseline. Some aspects may be harder to create and others might be easier to do by using a mundane skill. I'd use the same rules for any skill. If it would be a 5 athletics roll to create an aspect, it should be a power 5 air spell to create the same thing.
Don't allow zone-wide maneuvers on enemies. Only allow Scene aspects. If they want to target multiple enemies with a maneuver, have the use spray rules.
