So, I'm with you on what to do on the plate side. There are a lot of options, I think, to ultimately get the feed into my apartment. The problem I can't work out is the what you called weird. And it is weird. I think this is the key to the whole operation.
After more digging, I think that this is a tap. Presumably the signal is coming from upstairs and needs to be passed downstairs with minimal signal loss. I don't think it's a splitter because, from what I'm reading, a splitter reduces the signal by half. Which would suck if you were on the ground floor of an 18 floor building. Conceptually, this makes sense to me. However, that's all that makes sense to me.
Anyone have an idea of what I may be able to replace it with? I'll look again for markings on the plate, but I don't think there are any.