I don't know the answer to your question about further tuning your spam filter, but I did want to share something with you that might help in general.
As you pointed out, catch-all email setups are a major spam catcher. You indicated that you chose to "suffer" this "side effect" consequence in order to be able to "create emails on the fly", so I'm wondering if you know about DreamHost's support for "plus-addressing"?
Introduced a little over a year ago, this feature allows you to create addresses as you need them without having to use a catch-all.
" Who needs catch-alls? Notemail@example.com!
I think we've already had more than our fair share of totally awesome
features for the month of September, plus three days, but I've been
wrong once before (I'm sure of it).
Which is why it never hurts to add a few more not-your-run-of-the-mill
features. Say for example, this one... a feature I'm pretty darn sure NO
OTHER WEBHOST ON THE PLANET OFFERS. And I say this after literally years
Starting right now, all your email addresses have a sneaky new feature:
How does it work? It's easy! For every email address we host you can add
a + sign and then ANYTHING before the @, and it'll go to the same place.
So, if you have an email address like say:
The following addresses now all go to the same place:
What's the point of that?
Well, now every time you have to give out your email address to somebody
you hate, you tell them it's got a + in it and then some unique
And then when they start spamming you some day, you can easily set up
your mailbox to auto-delete messages sent to that address!"