So, going back and reading the rules on thresholds, it says that a threshold starts with a basic strength of 3, then gets +2 for each positive element that should boost it, and a -2 for each negative one.
So, perhaps with building a circle, to represent how potent they seem to be even with the simple ones done by guys like Butters, something like this might work:
At the end of constructing a circle via the most simple means, the user in question makes a Discipline or Conviction roll (I'm tending to lean towards the latter, but...), or maybe lore? or can use your thaumaturgy abilities if you have it; add the total result to 3 for the strength of the circle.
So, Butters invokes his "Polka Will Never Die," aspect and rolls his dice, gets a +2 on the dice, another +2 from his aspect invoked, for a net Threshold strength of 7.
Since a Threshold can act like a block, that provides for a really hefty block for him just standing there.
Molly decides to scribe a circle around a big horde of Binder's demon thuggie guys. She performs a manuever, "taking my time," and another, "I need to get this perfect!" on herself, then finishes the circle. She makes her roll, gets a +1, tags the two aspects for a net +4, adding that to the base threshold strength of 3 for a total circle strength of 8. Binder's thuggies dissolve into goo.
Dresden builds his spiffy metallic super circle in his lab, with aspects "Metallic Ring Crafted by the Fey," "Runed and Empowered," and "Carefully and Meticulously Constructed."
Or something like that.
Then when he summons something, he adds in those three aspects he can invoke to his Thaumaturgy checks.
Or whatever. I don't have my books on me, I'm sleepy, sick, and all that. Stupid allergies. So I'm stream-of-consciousness typing here right now. Ugh.