Title says it.
I would not invest what you cannot afford to lose.
I would not purchase without the understanding that the value of your purchase can go to zero.
I would not speculate on the assumption that the gains ETH has experienced so far will continue.
I would not throw money at a thing with no marginal utility if there are things with marginal utility to throw money at.
I would not purchase into the cryptocurrency ecosystem because others are, or because the hype is driving you, or because there are crazy riches to be had.
I would keep in mind that many responses you will get here will be from people that, like myself, invested in ETH when it was effectively a penny stock. Our investments are now large but our exposure is not. We can afford to be dispassionate about it because our money is "potential money" without ever having been "actual money." It's a lot easier to be casual about something when you can afford to lose it all.
The intrinsic value of Ethereum, as a technology, is non-zero.
The technological innovations of Ethereum, as a technology, are open and promising.
The community around Ethereum, while young, naive and outspoken, is also talented and innovative.
The network effects of the Ethereum Network, while modest compared to existing banking networks, are robust and expanding rapidly.
You should read this. I tell anyone who asks me about cryptocurrency that it's a wretched den of scum and villainy. I have zero evidence and nothing but speculation but that speculation leads me to believe that the Russians caused the Flash Crash because they could (put in a bunch of super-low orders on one side, dump a giant market order on the other side, collect everyone's tears and put it in your wallet). There is circumstantial evidence that an outage a month or so ago that saw the market cap of Ripple spike above ETH was due to coordinated DDOS and market withdrawals. Cryptocurrency manipulation is real, unregulated, and unstoppable and if you thought beating a market that's nominally "fair" was tough, try it when there are no rules.
But I still hold ETH. I intend to keep holding ETH. I think its value will increase. And frankly, the crypto nerds don't sound half as crazy as the goldbugs.
I told my father I'd made some money in cryptocurrency. He advised me to sell everything now before I lost my shirt.
"Now" in this instance was March and ETH had yet to broach $15.
Bitcoin went to $1000 before it went back down to $170. If I'd bought Bitcoin at $1000 and it went to $170 I would have been quite bitter. ETH could easily go to under $100 again. Like next week. Or tomorrow. But I don't think it'll ever go back down to where I bought it.
And I bought Bitcoin at $170.
Your mileage may vary.