An infinitely growing blockchain will inevitably fail by centralizing. Crypto-currencies as they exist today are doomed, but the protocols and tech created now may hopefully inform the design of something that is useful as a currency.

Also, high transaction fees make it useless for small (normal, everyday) amounts, so it can only be used as a store of value. It's really more analogous to gold or a stock, with the one significant benefit that it's harder to steal than gold and can't be ~~lost~~ stolen institutionally.