Depends what you mean by 'useful'. They were a technological marvel, but an incredibly inefficient way to deliver approx a ton of high explosive. But I guess we should be thankful that Hitler wasted so much of Germany's increasingly scarce resources on 'Wunderwaffe' like rockets. The Allies developed technology that was less showy, but much more useful (computers, cavity magnetron, proximity fuze, atom bomb etc).
Every new team has to start somewhere; even SpaceX had to learn to crawl before they could walk, and that was with the benefit of decades of prior art to draw upon. It would be a shame if SpaceX became the last company to ever succeed at designing a rocket because no one after them would try.
