I am coming to the conclusion that a simple word filter is not going to be enough to do the job. No matter how many words I filter out, there will still be plenty of spam coming in that don't contain any of those words.

As well as legitimate email that contains the words you're already trying to filter. I've long since come to the conclusion that word filters aren't the way to go about stopping spam. Proper spam prevention has to work on the mail server, not in the local user's mailbox.

My ISP has a quite agressive set of spam-stopping features running on their mail server, and I do manage to get essentially zero spam to that address. However, there is also the problem that their spam-stopping features sometimes kill legitimate emails, as many of my friends will attest.