@MiaSkywalker First, thanks for the compliments. Hydrangea Hedge is my favorite build. I had a lot of fun creating it.
Second, apparently I'd almost gotten there. I had those game backups that I'd forgotten about. And I keep a copy of store content in a separate folder to avoid downloading it again. But since my problem came when the Launcher started behaving erratically I'm not sure it had anything to do with user files. So, I thought, bite the bullet and do a reinstall. My one clear mistake was that I forgot to back up my current saves before starting that and lost my current game. (But, then, maybe it was user files and a quick swap out with a backup might have cleared it all up.)
From what I've been able to learn on the web, the problem is with how The Sims 3 uninstalls. Or, more accurately, doesn't. It leaves bits and pieces all over the registry that get in the way of a new installation. I'd always known this on some level because over the course of 3 different installations my computer has only asked for my game codes once. So I knew they were buried in there somewhere.
Anyway, what's done is done. Or, not done, as the case may be. I've completely backed up what is on my PC, Sims and not Sims. Tomorrow I wipe my system and reinstall everything. This is not entirely a bad thing. Because my primary drive is relatively small I re-route all non-Windows and non-Sim software installations to the secondary drive, which is slower. I wasn't fully familiar with how to do this when I first got my system and things were kind of messy. This gives me a chance to make a much cleaner setup. Once I have Windows updated and The Sims 3 installed and running I will run a full system image backup. Then if this ever happens again I can revert the system to a state where I know The Sims worked.
Everything else is both secondary and easier to install. Although, it would probably be nice if I could get Photoshop reinstalled before my online class at 2 tomorrow afternoon, I don't think that will happen. But that's okay, I'll just review the class afterwards. We aren't expected to have the program open during the lecture anyway. I just do it to help things stick.
Well, bedtime. I have a busy day tomorrow.