It's been my experience that supply demand imbalances that cause vol to go off mark are either short lived or extremely persistent. short lived are exploited by market makers, flow traders, and layoff accounts. It's tough for a trader whose not in the flow to exploit a lot of it. Persistent never go away and is WAY bigger than the vol market. I only find a handful of these a year and they generally involve some kind of fundamental event (biotech PDUFA or similar). Generally you're shorting into it which is scary.
And even more of these supply demand imbalances are efficient. Look at the term structure in HLF. From Feb to Jan14 the term structure is extremely inverted. Clearly there is huge demand for volatility in the front as this whole ackman/icahn thing plays out. But the market is quick to price the forward vol lower. It's agreeing with you that the vol is mean reverting and a lot of it is priced in.