Monopoly is such a pvp, take over the board, kind of game that it seems wrong to just play the game too accumulate cash. There needs to be some kind of antagonist. Monopoly is a zero sum game, to win monopoly someone else has to lose.
I would also suggest adding a save option. It is frustrating spending hours playing in endless mode to have the game crash and have no record of my game at all. Make periodic saves and then crashes are not so terrible. Shockwave is going to crash sometime anyway so lessen the pain. Nice game though. Fun and challenging.
This could be a really fun multi-player game. A character could check in at a tavern to hook up with players. Share quests and loot and when the character leaves they find another player. Could still have solo exping.
Might want to consider crafting too. I personally like to do crafting with my rpg. It seems to make my character belong instead of just kill things.