>> I've been doing this post series that I call "Something old, something new" <<

That's a good idea.

>>Well - it was meant to be at weekly intervals, but in practice it's been more like every 10-14 days. Or whenever I feel like I have something to write about.<<

Recurring posts are a good way to keep up activity on a blog or website. It doesn't have to be a tight schedule, although it can.

>> I will say, though, that no-one has seemed super interested in the posts <<

Have you tried putting a feedback question at the end? Usually people are more inclined to comment if you ask something like, "What are some of your favorite old or new things in this category?"

>> The characters are delightful and loveable <<

Not so easy to find nowadays.