Pfft...that would cut idiotic "nice project" posts down by 90% or more in that section, but unfortunately that's not where the problem really is.  If spam was confined to ANN threads, we'd be golden.

I doubt this suggestion will take seed, as Theymos wouldn't want such a function overused, thereby discriminating against noobs.  The best option is still to make threads self-moderated and to have enough balls to delete posts that don't add anything of value.