There are a great deal more than two kinds of anti-seize compounds. A quick look at the offerings over at MSC shows eight. I'm sure there are more than that, but there are at least eight that can be obtained easily (i.e. can be ordered from MSC/McMaster-Carr or something similar).
I've never seen nor heard of a glass based anti-seize compound before. Even the gray Permatex anti-seize to which you refer in another post is not described as such. Permatex says it's a "highly refined blend of aluminum, copper and graphite lubricants" on their web pages:
The copper kind is actually more common than you think, Permatex makes one and I've had no trouble locating it at any of a wide variety of chain automotive stores. It can also be purchased from any decent industrial supply as well, no need to hoarde the stuff. I wouldn't think globbing it on would be acceptable... it'd also be conductive, so you'd want to keep it away from the tip of the plug. Best to just use it sparingly and carefully on the threads.
But they also use metal as an anti-seize and anti-galling agent, which conducts electricity and would likely negate any insulative effects of the grease. A Teflon-based anti-seize, on the other hand, would probably do a much better job as a dielectric.
The one thing I'm surprised nobody has mentioned yet is a graphite based anti-seize made specifically for use on spark plugs like the one marketed by Champion, like this: