False Primary MX Record = MORE spam?

[Ben Hanson]

I spent some time recently reading the wonders of creating a false 
primary MX record (Nolisting).  Supposedly compliant mailers 
automatically mail to the primary MX record first, and then upon failure 
retry to the secondary, delivering to the real server, while 
non-compliant spammers just stop in their tracks.  This is supposed to 
reduce server load and therefore the number of messages SpamAssassin 
needs to examine.  However, although it is working in the manner 
prescribed, and I notice it has introduced a short delay in receiving 
mail, I believe my overall mail load has increased significantly.  It's 
not a big user base.  I was seeing around 1,100 to 1,400 messages daily, 
and now I am seeing around 1,600 messages or more daily going through 
SpamAssassin.  I've watched it a couple weeks just to see if this was a 
coincidence, but it seems constant.

Here's what I'm thinking.  Just for kicks, since it didn't help anyway, 
maybe I should reverse the two MX priorities, making my real server 
primary again, and leave the bogus entry as the secondary, just to see 
how the overall load changes again?  Might be fun, or even enlightening. 

Does anyone have any solid experience or beliefs of the effectiveness of 
these sorts or things?  Have spammers started targetting secondary MX 
records first?

Ben