I'm not sure you can separate out opinions easily from actions/decisions to spend money, and I don't find the idea of a rational market or a rational crowd at all persuasive. I'd say how they spend their money/resources has always been intimately connected with their opinions and (crucially) how they shared them. A few examples of the irrationality of crowds (NB I'm not saying they're always irrational, just that they're rarely rational/wise):

The expedition to Sicily by Athens in 413 BC The run up in the Facebook stock price on IPO day Widespread investments in failsafe CDOs pre the crash of 2008

If crowds have any wisdom, it dissipates pretty quickly when they gather and start sharing opinions.