I definitely felt that playing silver league made me a lot more money than AI3 ever did. I hardly had any upped cards and discovered the great deck Grabbix, that could pull off a 50% win rate in Silver League (that was a few months ago, though, maybe things have changed). And for me that was way more profitable than beating AI3 nearly all the time (with my old mono-life deck). Grabbix of course is a rush deck so games went much faster, too. The really fast decks are way out of my league with all those upped cards, so I don't know about them, the money Disc 'EM makes is impressive.
I posted after 200 games with a semi-upped Grabbix: 200 games, 123 wins, 15 EMs, 77 losses, 7 special spins, 7.49 ttw. Roughly 6000 electrum won (not counting cards, which actually I didn't count anyway.) Also, I didn't keep time, maybe it could be extrapolated from the ttw. I'd guess 8 hours altogether.
Though probably even more profitable is farming False Gods. That is, if you are prepared to sell the upped cards you win (or at least count them as your winnings). The last weeks I've only played Flay 'Em against the FGs, using the skip guide from the FG efficiency study. Theoretically it should net you 4783 electrum per hour. If you don't have the few upped cards (3 hourglasses) needed then go for the completed unupped Liquid Antimatter, which is only marginally less profitable. Both decks are ingenious and great fun to play.
