I post to OCD when it doesn't fit into another category I follow or know about - I'd rather use communities than just post to my blog. Is there another decent general one?

That is exactly how I do it as well. Not everything fits under these categories.

Probably not, but I'm sure there's a few that'll fit your random topics. You could also create one. Maybe PowerHouseCreatives as a general one?

We've considered doing this for those who post there "aiming" for certain big curators that I'm not gonna name but I'm sure we all know who that just seem to thumbnail vote on whatever has the lowest rewards thus far so they can maximize curation. Either asking them nicely first to post onto the other communities that exist relevant to their content or to start downvoting them a bit so the curators doing these curation maximization's are turned away and curate other more deserving posts and settle with an okay ROI.

If someone's posting in ocd just for the hope of a vote, I think they'll eventually realise it's not getting them anywhere and make move to a more suitable community for the topic. Could it be worth the community mods having a quick look through ocd's community periodically and alerting those posting to more suitable communities to put their work in?

Yes that's the plans. Thing is there's certain accounts such as @trafalgar that seem to vote on 10 posts per day at random in the community as long as they have minimal votes before his so he can maximize curation which in turn gets a lot of low effort posters to continue posting the same content over and over and they have no early voters for a reason... but yeah, some misaligned incentives that should be met with downvotes to encourage them to curate somewhere else or on better content even though they may not get the biggest returns it would be better than downvotes.

Of course, either way it would be a time consuming process. Maybe push the devs to add the ability to idle a Community?