The only limiting condition on thaumaturgy is the preparation part. If you wave that, you can just nuke everyone and everything with that 30 shift fireball, and quite frankly, that would be pretty lame (unless that becomes part of the story, but then the story would be about the wardens trying to stop that madman with the magical grenade).
I thought about it a while ago, and back then I thought, that I might be good with keeping the shifts that would be logical to keep from the preparation, for example Lore rolls to get the specifics of a magical circle, contacts for someone to show you how to get to a specific location, etc.. But there is no preparation roll, you can't justify to do again.
If Lore discovered the specifics of a magic circle, you would still have to draw it again, still using Lore.
With contacts, maybe you need to talk some people into letting you to that location again, or you know the location, but would have to use resources now, because you need to bribe someone to get in.
Any other way, the spell becomes a plot device, and the story should change to how everyone else reacts to it.