Unfortunately I think spam must still work, or spammers would have stopped sending it. They're pretty pragmatic. It wouldn't take more than a couple months of making no money before they switched to some other racket.
Plus GMail is a bit strict. I still get lots of false positives.
Nowadays, setting up a good spam-protected mail server isn't very sophisticated anymore.
In our company, I'm running a plain Exim mail server with a SpamAssassin in almost default configuration and some standard RBLs. Although I have a quite burned email address, I'm getting just around 5 spam emails per day and false positives are rare (less than 1 per month, I guess).
If we had (all of us) the parent's point would apply: spammers would not be making enough money since no-one would respond. So for some people, spam is still a problem when are fooled by scams.