Thank you ! That's really helpful - I can see I should increase the breadth of comments (which is something I always find easier than writing posts anyway), and focus in on actual posts in just a couple of communities. I hadn't thought of it from the timing point of view.
Something else I'm doing is creating a document that can be easily accessed from each of my PC's where I can note down ideas for posts, or even snippets of text. That way, even if I don't have time to post right then (as in... I really ought to be working...), it reduces the number of times when I feel like writing something but stare at a blank screen wondering what to write about.
Also, thank you for the follow !