Well there are many opinions about this subject.
I find hard to believe the supernatural spirit guide, but I don't underestimate the dreamguide either.

Even if DG is just a creation of our subconcious can be really helpfull. Our subconcious is free from society rules and can be a good adviser sometime.

Does our subconcious knows better science than us? Actually yes. Einstain use to think about hard problems in hypnagogig stage.

Can predict the future? I don't think so, but I m not sure. Freud -father of psychanalysis- claimed that when we dream we can develop some kind of telepathy.

If you DON'T know something, your DG doesn't know it either? well I m not sure, because your subconcious don't forget, your consious forgets becouse of fear or bacouse have other priorities.

Well like I said before I don't believe in supernatural. But I believe in "supernatural" power of our own brain. You never know the possibilities. And I think tha DG is very cool think to have anyway. Whatever you believe it is. Don't miss that.