Annual returns for classic Hermes Birkin bags beat returns for S&P 500 and gold, a Baghunter study found. Luxury bags saw average annual jump in value of 14.2% between 1980 and 2015 compared with S&P's 10%. Experts warn only select bags appreciate in value, and unlike stocks, bags don't pay dividends. Some experts say handbags are among least volatile assets.