It makes sense to build the houses and cars now, when the cost of doing so is relatively low, rather than waiting. And building them now has kept more people employed and reduced the risk of deflation.
Whether or not he grew fond of Frankfurt, his work as an advisor to the Executive Board of the ECB seems to have been an important step towards new tasks after he returned to Madrid. In 2007, he became the head of the economic policy division at the department of economic analysis and forecasting.