I honestly like the idea of purchasing btb directly, it's something to be considered. (Not that I'd ever find myself buying btb, way too broke for that.) In a sense, btb already has a good amount of "real world value". People sell demo codes on here often, which could be considered something that'd be paid for with real currency, in other communities. There's also a couple of pokemon shops here, which means btb has value outside of just the AC series. Selling btb could only be beneficial, the site would make money for further improvements without excessive advertisements, and it may help prevent scamming immensely.
I do only have one worry about it though. If buying btb becomes a popular thing, then the "economy" that has been created might be disturbed. The value of btb would go down. But then again, this is not neccesarily a problem. In fact, the value btb going down may even be considered beneficial.
Lots of people buy btb, and tbt makes money. Since so many people bought btb, the value has gone down because there is more going around. Since the value of btb has gone down, people want more btb for whatever they're selling, so everyone posts more to earn more btb. Now tbt is not only more active, but they've also got money to spend on improving the site, advertising the site, and possibly even doing AC related giveaways. Everyone benefits.