Sounds like you have a beautiful home. Converting a small bedroom to a master bedroom suite would generally add about $60,000-$85,000 to your home's value. I use the word generally because I am afraid with the improvements you have already completed and your current ideas you might be over improving your home for the neighborhood. If you plan on living in your home for another 10 years, I would say go for it, but if you are doing the addition and then sell I would like to see your your home before I give you the go ahead.
Feel free to call to set up an appointment. My toll free number is 650-877-Lee-Sells.