Mass adoption should indeed provides more stability to the prices, talking mainly about the big crypto-currencies out there. The volatility of nowadays can be explained by the fact that a total of 1000 people own 40% of the Bitcoin market right now. I believe in 2 years time price should get more stable, and therefore could attract many investors who feared this volatility so far.
But big ups and downs will still happen on crypto-currencies with small market cap. I wonder if regulations being implemented more and more in western countries will make it impossible for small (new) crypto to emerge.