Google is very successful in rejecting spam before acknowledging its reception via SMTP (probably mostly via IP blacklist) so I don't see it, the amount of spam shrank drastically. For a very long time a lot of spam came via icq@mydomain (yes, it has been a while), but nowadays almost all spam that I see comes via the @web.de address where Google cannot apply its IP blacklist because its received via web.de's servers. I know because the mydomain email server also used to forward received mails to Google, resulting in said 30k entries in the spam folder. The transition to put Google itself in the DNS record made all the difference.
I am kind-of surprised I don't see more spam coming via the catchall address. Sometimes spammers use mydomain with random local part as sender address, so I get bounces.