As I was reading a thread on sight reading, I'm wondering, with hymns (which I'm not trying to be able to sight read yet), is there any disadvantage or advantage to working on hands separate v. together?

If you cannot sight read hands together, then you are trying to sight read something that is too hard for your ability right now. The whole purpose of sight reading is to that you can play the piece reasonably well the first time you've ever seen it. So that pretty much precludes hands separate work. Hands separate is a great tool for learning a piece or working on it, but shouldn't be used in sight reading.

I've finally learned Nearer My God To Thee (after 3 weeks)...still, I can see that it might get easier with time.