This is already possible with trophy points in regard to your first paragraph; however, since you want something more advanced, if you could provide an example, like a mock-up, of what you'd want it to look like it, I may be able to find an add-on that accomplishes what or close to what you want.
Sorry for not being as detailed.
I ran a board years ago. I can't remember if it was phpbb or SMF, but it had a currency system that would award activity points for new topics, new posts, daily login, daily visits etc. It also came with a small virtual store where the user could buy things like icons for their user card or profile. It also had a raffle/lottery system built in as well. Was a nice little activity system that allowed users to redeem their activity points and also allowed the admin to hold contest with site currency as an award. Not sure if Xen has anything similar to this or not.