Purples? You should make people buy fake currency like MS points or a real world example, casino chips. People are far more likely to spend money when it's not really money. That way you're not doing micro transactions all the time.
That's a good idea, I'll definitely do that. You think I should still charge the monthly membership fee or just sell point packages?
I'd just sell points. I've stopped my xbox live subscription for example, but a quick tally last night shows I've spent $500 on the marketplace! If you'd ask I'd have said I'd spent about $200. So points are definitely the future.