I just stumbled upon your ELO system 3 days ago, and as i am good with math and enjoy developping systems myself, i found yours to be very effective with premier League and bundesliga. Not so much with the romanian one (where i'm from) or polish.
Anyway, i just wanted to let you know that i applied a tweak to it, and when the elo differential is anywhere from -15 to 10, i bet it will be a draw. If the elo difference is > 30, i bet with -1 handicap, and if it gos >70 -2 handicap, >100 with -3 handicap. These tweaks increased the earnings by 100% in the bundesliga, and only a couple percentages in premier league. I also found a high increase, somewhere around 50% in Argentina.
I will do similar tests on the rest of the leagues and will let you know of my results, if you are interested that is.