What is the point in having a vBookie system if we cannot spend our credits on anything?
I love the betting idea, but meh, what's the use in it if we get no reward from the vmoney we have earned from gambling? It's pointless.
What I suggest is a vShop, I have seen this on other vbulletin forums I am on, and it allows the user to purchase some cool customisations with the credits they have, eg. coloured username, bold username, more customization with sig etc.
You should explain in more detail how their vShop works and what people can get.