Ack, I've only got like 4000 gp right now on my iD L, you can only earn 200 gp from winning a game. Ichiro, How did you do it? xD
I earned 99,999 GP on my 10-11th generation. It does take a long while but the principle is basic - avoid feeding your Tama snacks to fill up the Friend meter.
And I've got a lot of playtime with it, particularly during morning/afternoon commute.