@svelasquez123: Argh. I'm certain I tried cycling the phone before this, but on a whim after reading your post, I cycled again and everything's working. That simply can't explain why the cloud collection stuff started to work, though.
Well, I got something out of posting this, even if I'm still left with more questions than answers and features that I can't use on all devices. Thanks.
Edit: By the way, it's clunky, but you can create playlists. Add music to Now Playing, go to the Now Playing queue, and there's a menu option to save the queue as a Play List. http://www.windowsphone.com/en-ca/how-to/wp7/music/create-a-playlist That link is talking about WP7, but it works the same on WP8.