Interesting point. There is a school of thought that frequent, shallow and short recessions are preferable, because if you don't have them you will pile up problems that all fallout during a deep, long depression. If this is true, then as you say, the skyscrapers, ridiculous art prices, etc. are just the most visible indicators of "lots of easy money, being spent stupidly", which is both a result of prolonged financial security and a bad omen.