The sheer volume of books I might be interested in 'finding' through BookCrossing are almost always in another city, another state, another country - but the folk at BookCrossing are usually quite talented at reviewing, and when I read those, I'm sorely tempted to buy the books instead - and often do.
There is very little different in the BookCrossing site than in a library, or a used bookstore - except that BookCrossing itself is a very strong "word of mouth" system, far moreso than a library. Think of the potential readership of people that just heard your name for the first time - associated in a forum where you insulted them. Will that prompt them to purchase your book?
Instead, a positive review in the book chat forum, or seeing your title in the "last released" or "last caught" column might have piqued someone's interest, and upon reading the review, they very well might have gone and taken a look in their local bookstore for a title.
I sincerely wish that you'd have taken a better look around, and that you'd read the sections specifically aimed at publishers and authors, but if nothing else, I just wanted to put forth that your opinion of BookCrossing as a place of literary leeches is very far off the mark - I've bought *more* books since I joined BookCrossing, not less.