I run our town website. 1,000 registered users but very, very little spam - over seven years I think I can count the amount of spam from China and Russia on the fingers of one hand.
Two reasons. One: a completely bespoke system, hand-crafted from finest dodgy Perl and inefficient SQL. Put simply, if you're not running phpBB or something well-known like that, they're simply less likely to find you. These guys search for phrases like "powered by punBB" to find targets.
Two: postings in the news, events and ad sections require approval before they go live. Postings in the forum don't - but you can only get access to the forum by clicking through a JavaScript "I agree not to be a dick" page, which sets a cookie (yeah, I know, accessibility yadda yadda). So, again, they're less likely to find it because it doesn't show up on Google. (Oh yeah, not having frickin' Googlebot hammer the server is a plus, too.)
I realise this isn't an option for everyone, but the OP sounds reasonably tech-savvy so should be able to do similar.