I used to believe Bitcoin was a mania too until I bought some and started playing with it, sending it back and forth across the world with minimal effort and saw how secure its blockchain is. That's when I realized its potential.
Just as a Gold replacement it has a great future, imagine if we add all the other cherries on top (remittances, smart contracts, micropaymets etc)!
I still own some Gold, but not much, the bulk of my savings have been moved to cryptocurrencies following this passive indexing strategy: https://steemit.com/bitcoin/@cryptoeagle/great-time-to-pick-up-cheap-alts-what-percentage-should-you-invest-in-each-to-become-a-multi-millionaire-a-winning-index
The main characteristic of manias and bubbles is NOT that the goods / assets are expensive, it's that they are OVER-valued. In that sense, we now have real estate bubbles in various cities and countries, a stock bubble in the US, bond bubbles everywhere, and various other sorts of bubbles. It's been said, correctly, that we are essentially in an "everything bubble." And the bubble will burst eventually.
On the other hand, it's not clear (and probably not true) that cryptocurrencies are over-valued. Was bitcoin over-valued at $100? Apparently not. At $1000? Nope. At $2000. Doesn't seem so. And we can make a strong case stating that cryptocurrencies are in fact presently far UNDER-valued.
As for precious metals, I still hold more gold and silver than bitcoin. With the price suppression over the past few years, it was clear that they were under-valued. So, I bought more and more insanely inexpensive silver. Kinda wish that I had bought more bitcoin instead.