Houses in dreams are familiar symbols for the self. Dreams of finding new rooms full of hidden treasures, accordingly, suggest a rich and fruitful area of self-discovery.
Because you are discovering hidden treasures from your past, your dream indicates an effort to regain a wealth you once possessed. For example, if you sacrificed some of your personal goals in the past, in an effort to meet the demands of everyday living (career, becoming married, raising a family, etc.), these dreams may be encouraging you to re-open "lost" areas of interest. (Is it time to sign up for those voice or dance lessons you always wanted to take?)
Instead of representing lost money or an overlooked inheritance, the hidden treasure of your dreams almost certainly represents areas of your life that used to hold a great deal of value for you -- that you feel you have become separated from over time. In order to locate these lost rooms, why dont you make a list of goals you had when you were younger that you always wanted to see realized in your life? Your dreams are encouraging you to reconnect with some of these younger, life-long goals and values. If you follow your heart, you will wrest these hidden treasures away from your dreams -- and into your waking life.