In the past you wouldn't put your money in something you believed it would grow faster than. And if you get a chance to make it, you'll be able to make it, with a higher level of risk than before. If you're worried about investing in this thing, I'm afraid the world is much less scary than we thought! To me, investing on a market is like investing on a stock or bond where there is a risk component, but it's also a good way to increase value through the investment of your time. You can make big investments when they are easy, but if the future is uncertain, then you'll have a real life time risk to be managed. If you have problems on your side and are not able to solve it, there's very little chance of a positive return (or loss). So a market is not a guarantee of being a good investment. And in any case, most people (including me) are afraid of risk in the markets in general.
Perhaps you're right though, and this has a long way to run... I'm afraid I just can't bring myself to invest in things which are overvalued due to FOMO rather than actually making money or having a prospect of making money. Old-fashioned I know.
Re pulling out of NASDAQ, I'm not sure that's a good example. You never made it back implies you lost something. You might have had indifferent returns in other assets, but not a loss. If you invested in 1999 on the other hand, you made a loss till 2013, over 10 years later, after another bubble burst. To me it is more important to avoid risk of extreme loss than attempt to chase extreme gains.
The Shiller book on Irrational Exuberance is better than the Greenspan movie IMO ;)