Well, I suppose the correct answer is that for a given technology T there is a window W in which T causes value to increase, after which T causes value to decre

Well, I suppose the correct answer is that for a given technology T there is a window W in which T causes value to increase, after which T causes value to decrease. The slope of the value increase from the moment of installation I to the end of the window, I+W, is probably quite steep, then levels off, then, at W, declines at first slowly then after some W' (the moment of real obsolescence), declines precipitously, and declines below the original value V. In other words, that Nest has/had appeal for 1-3 years, after which it is/was yesterday's news. A house sold during those 1-3 sells for more because of the Nest, but, if sold afterwards, sells for less (adjusted for other market factors) because of it.