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.
Thank you so much, and best of luck to you, sir!