I'm impressed by your system of deducing how popular different pairings are! Using only LJ feels limiting though (this while acknowledging that there have to be limits, otherwise you'd spend three years going through the internet to find fics). Hypothetically, it might be useful to check every Snape fic on fanfiction.net and see what pairings people write there. Then you would have two sets of data and could compare them. On the other hand, it might take forever and it might not give us much new information, since ff.net is just another site and not really representative of fandom as whole.

I think the 'division of labour' statistics are fascinating. You said (IIRC) that one dojinshi can set a trend -- is the Snape characterisation in the dojinshi you're studying consistent? In other words, is Snape uke in those 94 stories in the same way? (I hope you know what I mean, because what I'm saying may not make much sense...)