Actually, I have more money than I need for promotions.
With a GM merchant, I get tons for all the treasure I pick up.
While it may run 20k gold to have everyone go up a level, I am getting more than that off the critters they toast.
Yes, higher levels cost more to promote, but the higher you get, the better (and more valuable) loot you get.
And yes, the developers released the game with the bank "feature", and yes, as a result it's fair game to exploit, though I doubt anyone believes this was intentional on their part. It's just one more bug (out of many) that wasn't fixed when they rushed the game to the market when it should have been in beta testing.