I have encountered the same problem myself. I've switched to linking to an image of a new disposable email address. Zero spam since then. (Actually, zero non-test messages total since then, but that's fine too.) I suppose that will work only as long as not too many people do it, though.
However, there are legitimate companies hiring through those threads. I know someone who got their current job from one of those threads. If you can avoid the spam, I think the benefits outweigh the downsides.