Altcoins are useful testbeds for proving features that can't be easily included in Bitcoin due to any number of reasons. Altcoins with useful features that cannot be easily incorporated into Bitcoin will have value.

As far as practicality, it's too early to tell. For example, Litecoin continues to be useful despite the fact that isn't accepted by many merchants. Why? It allows for the BTC chain to be broken for money laundering privacy purposes. In the future, perhaps Monero will provide a superior privacy feature, even if Bitcoin is used on either end, because it breaks the chain of transactions.