The startup community needs to get over the idea that "valuations" are based in reality. Rich people need ways to get richer. They could choose tech startups, they could choose real estate, they could choose tulips... it doesn't matter as long as they can make up money and push it back and forth between one another.
But alas, it feels much better to say "My company was valued at a billion dollars!" than it does to say "Rich people used my company as tool to transfer money to each other!" If we would just stop taking the numbers seriously then we could stop the debate about whether or not we're in a bubble.