The odds of spammers having any canned solution for us is basically nil.
Even after a year, we'll still be a small fish.
On top of those facts of life, we built Stack Exchange as our previous project, which unlike Discourse allows completely anonymous, no-login-required participation. A far tougher scenario, since anyone could just start typing in a text box right now and spam away to their heart's content.
Do you see any spam there?
I rest my case.