I don't have hard evidence to back me up, but I've been on the site for over a year now and this has come up many times. As far as I can tell, we haven't come up with anything conclusive, but here's my logical thought process:

Most of the reason for needing sleep is to recover the energy that your body uses up. You see (if I remember correctly; I had to study a chart for school once) your body is constantly gaining and losing energy, but during waking life, your body can't gain enough energy to make up for what it loses, so you sleep to recharge. Now, I imagine, the part that the brain needs is a very minimal part. You could probably make this up in your Non-REM sleep, in which you are highly unlikely to have any dreams requiring too much concentration to the brain.
So, to answer your question, if you did NOTHING but lucid dream while you were asleep, it probably wouldn't be good for your health. But, otherwise, you should be fine.

Also, nice to have you back Sleepy. Hope you stay for a while.