While I'm in a "cleaning up" frame of mind I decided to get rid of the Ultimate Category Excluder plugin I was using to split old posts into an archive.
Instead, I now separate them using a simple if statement at the same time that I exclude microblog posts from the main feed:
if( !is_archive() ) {
set_query_var('category__not_in', array(81));
// Exclude from all but archive pages
}
Having a plugin installed just to achieve that is wasteful and an overhead I can do without, but it also makes me realise how much has changed since I first added the microblog.