It is true that mirrors were an expensive luxury item in France at the time the Hall of Mirrors was constructed in the palace at Versailles. The decor is certainly a commemoration of the superior status of French economic, political, and artistic accomplishments of the era. Venice was considered to be the European center of mirror production in those days, and the fact that the mirrors at Versailles were manufactured in France was a challenge to Venice's claim of superiority in that industry.
There are over three hundred and fifty mirrors bedecking the walls in the Hall of Mirrors, and it has been the location of lavish balls and ceremonies throughout history, including the signing of the treaty that ended WWI.
Louis XIV walked through the Hall of Mirrors daily, but it seems short-sighted to say that he had it built simply because mirrors were expensive. It seems more likely that it was an opportunity to feature Parisian workmanship and create a lavish display that demonstrated French prosperity in his day.