Depends on your definition of 'usefulness'. Getting around strict capital controls (e.g. China), politically motivated restrictions of payment processing (e.g. donations to Wikileaks), or legal restrictions (e.g. dark net marketplaces) are clear cases where decentralization is useful, I have little doubt about that.

Whether there will be a wider appeal than the cases above (e.g. contracts in general that are not subject to enforcement/regulation by a central authority, or the often invoked 'store of value' usage case) is something we're in the process of finding out. I don't think it's a given those broader usage cases will be based on the Bitcoin network, and not some other (possibly centralized) crypto, but I'm also pretty skeptical towards the opposite claim, that it's a given it won't happen. Hence, speculative activity all around.