Wouldn't you want the spray before the sc because thats where all the heat comes from and right there while its being generated most of it will be gone also if sprayed into vacuum it will atomize better and scavenge from the reservoir in boost raising the line pressure?
Some people spray before the supercharger because they have no choice (GTP, Lightning, Cobra ect ) I have hear of only one person spraying before the supercharger with an SC, and he used a dual nozzel with minimal spray to get a better seal on the rotor to case clearance, then used a second larger nozzel before the intake manifold.
Claims it added over a pound of boost. My concern would be keeping the mist in suspension thru the supercharger, upper IC tube, the intercooler, then uphill thru the lower IC tube and finally down into the intake manifold. Spraying before the IC also creates the possibility of puddling in the lower tank of the IC. It's not really a problem with the cars mentioned above, because the supercharger exhaust down straight into the intake manifold.
On an SC or other cars with similar tube and IC configuration, I think it makes more sense to let the IC do it's job and remove all the heat possible, then spray the methanol just prior to entering the intake manifold, like you would if using nitrous. That stuff you said about being sprayed into vacuum and scavanged from the reservoir isn't going to work like that.
PS: I'm using the Snow Performance system on both my cars.