I think that dreaming occupies a fairly small time period compared with sleep as a whole so it has very little effect on our ability to rest. During REM sleep our brains convert the short term memory of the day gone by into long term memory. This by definition requires the brain to "work" rather than "rest". If it did not do this then we could not function normally as we would forget many important events. This conversion is much of what we interpret as dreams (not all of it, some dreams are just random stuff) and so whether we have lucid dreams or not, our subconscious keeps this process ticking over. Plenty of time during sleep is devoted to rest and recovery but REM cycle sleep has many other important functions. I would not worry about this as it is a natural process. Your mind will not let you screw yourself during sleep. What you do while you are awake however is your business. The wakeful processes devoted to inducing lucid dreams are far more likely to be of harm. For example, if you spend too much time reading about how to lucid dream at work you might lose your job