When the market dumped, a lot of properties were scooped up by investors and became rentals. It's kind of like when you get an easy commute because it's some obscure holiday. It doesn't take a lot fewer cars on the road to ease the congestion dramatically. Since a good number of single family homes were taken out of circulation, there are fewer homes available to buy. This, along with low interest rates are goosing the sales prices of existing homes, IMHO. If all the investors decide to sell at the same time the rates increase, i.e. better opportunities for investing, then the shit could really hit the fan. One without the other worries me less. That, and the fact that I'm not counting the value of my paid-for home in my net worth.
While I'm thinking about this subject, what worries me more long-term is the number of millennials who do not plan on buying homes. In my town, they are building crazy expensive apartments everywhere and the young 'uns are snapping them up. If this continues for long, it could most definitely have a negative impact on prices. Time to buy apartment buildings, I guess.