I do believe ETH will reach a lot higher than it has already but at some point will be replaced by other smart contract capable blockchains for various reasons. I think most of the value comes from the confidence people have in Vitalik and the media coverage he has had, the create your own token issuance (ERC20) and the smart contract language (Solidity) being developed by the Eth team.

You will very likely be able to make financial gains on ETH for a few years to come.