According to Tibetan dream yogis the awareness you need to have to know that you are actually dreaming, is the same you need to have to be able to tell that you are dead... so if you believe in that, then yes; LDs are a preparation for death.

You could also read the mammoth book by Thomas Campbell called "My Big Toe" (Theory Of Everything) to maybe get a clue of whats to expect after this earthly life ends.
I would say that Lucid Dreaming could be a way to experience one form of "Non-Physical-Matter-Reality", but a reality without any rules as opposed to other forms of NPMR where some rules apply.