1)Our society is structured in pyramids across multiple dimensions. On top of the these pyramids are powerful cliques. The pyramids that are predominantly influenced by the business world have even stronger cliques at the top. People at the top try to optimize for their success, and its only human. So ya, this who pump and dump is not surprising, happens everywhere.
2) Mailbox is a super-sexy acquisition for Dropbox. Because of my work, I am in this unique position to look deeply at around 70 online backup and cloud vendors, their features, their social signal, their pricing etc, their usage scenarios, their usage feedback and I think, given the uber-competitiveness of the space, most of these vendors will either a) move upstream and try to increase the real estate of their clients (Box trying to get into document editing suite is a prime example) or b) have a differentiated offering like egnyte. With this context, I think, the mailbox acquisition is an absolute bomb. I am doing further research on this topic and will hopefully publish it soon.
So yes, the hype-cycle was at work, but its normal and dropbox founders and executive team were pretty much certain they needed to this.