For it to be a currency retailers have to accept it as payment which some do but it is not widespread. For it to be an asset is has to hold some value, gold, for example, is a store of wealth there is a limited supply of gold, it cannot be created into existence like fiat money or cryptocurrency.
Sure some will argue that bitcoin is a currency but when in reality all of these coins are money rather than currency.
We are about to start accepting bitcoin and ethereum as payment for our services here in the UK maybe possibly accept other coins too.
What gives these cryptocoin value? nothing s far as i can see other than we have agreed to a coin is worth x or y amount, the expection to the above are when coins have a purpose like steem, musicoin, bitcoin and ethereum, most of the othercoins are generally considered scam coins.