French Business Spam

Two to three times a week, I get mail that starts something like this:

Vos projets sont plus nombreux et plus complexes que par le passé !

Yes, it's French business spam, which evades the spam filters because its written in French. I get it because my regular email has a .ca extension which means I could be from Quebec and I have received email from friends in Quebec. It's selling some conference somewhere in Quebec. I try unsubscribing and adding the addresses to my spam filters, but the messages keep showing up, two to three a week. What else do I expect? They're spam. What I don't understand: do these messages work? Are there Quebec businessmen who show up at these conferences because of these messages? There has to be some point where the cost of sending outweighs the benefit, doesn't there? In the meantime, I guess I should be grateful it isn't worse.