I'm reasonably certain there are bubble elements. ICOs with little more than a whitepaper and a product roadmap have tens or hundreds of millions of dollars, and the market cap for some of these coins belies belief.

However, on the flip side Bitcoin and altcoins are just starting to gain traction amongst non-developers as useful items. Once the mainstream catches on, money will come flooding into the space driving valuations even higher (also note that thinking about bitcoin in terms of market cap is a little weird. It's like thinking about the number of US Dollars in circulation as a marketcap. Bitcoin is a currency not a revenue generator like Siacoin or Golem).