This is a tiny update, that sadly ended up being rather over-sized on disk :(
So. What happened?
Traditionally Unity sets all imported images as DXTC1 or DXTC5 compressed textures. These have a lot of advantages in terms of loading speed and in-memory size, but they are rather heavily compressed. That's a tradeoff we're usually fine in with Textures used for 3D images, but it can be an issue with 2D images (which is the way I'm using it).
I made a test-case changing it all to lossless compression (so the images don't get any 'jpeg' style artifacts), and I decided it was worth doing that across all the platforms once and for all. I hadn't fully appreciated just how much work was involved in that :)
So far, Love of Magic, Morningstar and Wings of Empire have all gotten the decompression treatment. Across 3 platforms (Windows, Mac and Linux), At 10-16 GB/platform/game (~200-250GB in total), my poor PC's gotten a real workout. But it's done.
TL;DR: sorry it's such a big download, though hopefully it should improve image quality a bit, and remove unwanted compression artifacts.
I'm hoping no further issues show up with Morningstar or Love of Magic, letting me focus fully down on Wings of Empire. Ad Astra per Aspera.