Greason notes that “prizes are useful drivers and are most usually found where there's some technology challenge or where there are many wildly dissimilar ideas about what's the best approach.” However, he adds that the value of the purse does not always scale to the task, and vice versa. “If you need $1 billion to win the prize, then it's simply not open to the guy in the garage—it's not going to work.” The contest “gave a focus to Burt Rutan and his team at Scaled Composites and who knows whether they'd have got Paul Allen [to back the venture] without the impetus of the X Prize,” he adds.
X Prizes are also “a great way for governments to simulate endeavors without picking winners,” says Greason who points to NASA Centennial Challenges and the Lunar Lander concepts that came out of it as an example. “Bigger projects respond more to market stimulus than one-off prizes, and NASA's Commercial Orbital Transportation Services is a better model for that.” Branson adds, “some people say prizes are less effective at really large sizes, and I suspect there's some truth in that—but I think there is still great room for growth in terms of offering more prizes in more fields.”
Allen also attributes the birth of Stratolaunch to the X Prize and the successful flights of SpaceShipOne. In a statement, Stratolaunch says that after the final flight, Rutan and former NASA Administrator Mike Griffin “began discussing the potential for a follow-on, orbital system. Paul Allen expressed his interest in funding the development of such a system as a means of reestablishing U.S. leadership in space launch and continuing his legacy of privately funded spaceflight.”