I bought about half of the speakers I have owned as demos. Saves money. If the place you shop has high quality electronics, I would like to see them damage a speaker just by playing it loud. It is many times harder to damage a speaker with too much power than with too little power. Plus, if they give you the full warranty still and something does go wrong, you get a new set of speakers. I don't see how you can lose. If they are as good as you say they are, they will last 20 or 25 years, so 3 times the use up to this point should have no effect.
Buying Dealer Demos
There are great deals to be had by buying speakers that have been used as dealer demos. The upside is the price, as well as the fact that you get the full warranty and support of your local dealer. The downside is if these speakers are used as the dealers main two-channel demo system, they will get usage in one year equivalent to 3 to 4 years in my home. The speakers I am buying are very high quality speakers, and have been driven by excellent electronics. They also sound great! Should I be concerned about the overall lifespan/performance of these speakers?