I'm not surprised that someone else has monitored trends in this fashion before, in fact somewhere in the cobwebs of my grey matter I'm pretty sure I've heard of this Elliot fellow and his stock market Wave Theory. I suppose I will have to cite him now whenever I refer to my own Wave Theory(1), for fear of reprisal from Mrs. Hammond and her cadre of MLA plagiarism police. (That's right, I worked cadre, the MLA and Mrs. Hammond into a football blog. Have the box top THAT!)
I'm thinking that the stock market WT is very macro in scope, and although the premise is similar - emotion/psychology will overvalue/undervalue something - I think that in reference to sportsbooks, it could happen on a more micro level. Sort of like day-trading.
Anyways, this is going to take some research and some spreadsheet jockeying, but I'm betting there will be some trends, amplified by the fact that gamblers are inherently illogical people (case in point, the house always win). I like your idea of keeping track of the lays, also. Getting historical data might be tricky, i'm not sure if this information is published anywhere, but I'm definitely going to keep track from here on out this season.
(1) Elliot originally coined the term Wave Theory in his stock market theories.