I thought I had already started a thread on this, but I can't find it, so perhaps I just thought about starting one.
Inspired by Timothy, I finally decided to use A+ content. I used to somewhat similarly to the way he uses it--as a way of displaying the multiverse and what role each series plays in it, with some teasers and a few notes about reading order. To display the books, I used a bookcase stock photo with the cover photoshopped on to it. (The sizing in A_ is finicky, but it's easy to make things fit once you get used to the specs.)
Did it make a difference? Yes. It's hard to say how much, but three books in the related part of the main series (bottom of the series page, not covered by the buy-the-whole-series button) have started selling from time to time, which they hardly ever did before. That probably means people noticed them in the A+ content in ways they didn't notice them at the bottom of the series page.
For overall sales, it's harder to tell as mine started slumping in late spring and are only just now reviving. (Practically every title I have sold at least once in the last three days, with 17 going out today.) Unless AMS claims credit, I think the lion's share of that comes from promoting on Substack, but as the three former never-sellers were included in the rush, other books may also have been sold through A+