"One of the things that always comes up in my mind regarding this is the concept of space relative to these other worlds. Does it make sense to say that they're "ontop of us" and out of phase so we can't see them, or do they propagate "sideways", or is it nonsensical to even talk about it?"

It's nonsensical. The space that we see is just an artifact of a lower level of reality. See http://www.acceleratingfuture.com/tom/?p=124.

"And you should always take joy in discovery, as long as you personally don't know a thing."

I generally give independent, replicated discoveries the same "joy status" (if that makes sense) as first-time-in-this-branch discoveries. However, you should take a hit when you're just rereading someone else's work, which isn't as challenging, or as fun.