Tumblr also has an "ask" field which could be used for sending in suggestions as well... though there'd have to be someone on wheat / chaff duty, and expecting a good deal of chaff.

Having the system require ongoing maintenance in order to have any output at all is a weakness. Also, having hand-submitted 'horoscopes' posted in order, as tumblr's submission function does by default, removes the randomness element and makes it much harder to include older concepts. It might work, but it wouldn't be all that much better than just keeping an eye on the new posts here, I expect.

My idea is to have tumblr just serve as an output system, and have a separate program that procedurally generates horoscopes from a list of sentences and then use email publishing or something to post them. That way it only needs attention when new things are going to be added to the list, rather than every few days.

As for rebranding...

I like "Actually Useful Horoscopes", if we're keeping the term 'horoscopes' at all.

P.S. Do tumblr rss feeds work properly for you? I'm subscribed to ~one but it spams me with updates when all that's changing is the number of comments/reposts. Am I doin' it wrong?

Yeah, I've never had a problem with it... are you sure you're using the right feed url? It'll be something like http://example.tumblr.com/rss