I'd recommend you look into switching to using GMail for your domain (I'm surprised DreamHost tech support hasn't already suggested this, since it is their preferred email setup now).
I use GMail to handle my domain email, and I receive about 1 un-filtered spam per week (and maybe one false-positive every 2 weeks, but so far only on mailing list traffic). My email address is posted publicly, and I use catch-all email for the domain. My spam mailbox grows by about 60 spams a day (presumably my domain actually receives many more spams - only borderline spam messages are held in the spam mailbox for review.)
You could probably test with GMail by forwarding one of your address to a free GMail account. Once you are satisfied, you could switch your whole domain to GMail (which has a limited, but free, domain service).