It just begs the question, why bother reno'ing/developing if you can make that kind of money doing nothing (apart from impecabble timing - but, IMO, not really that hard too)...
But it would have gone up by this amount without doing the reno anyway, that's the point, the market in this sort of suburb moved by 30-40% in this particular time frame (from Dec '08), whether you value added or not.