What science demonstrates that running on springs would be beneficial? Basically the runner and his or her shoes is a closed energy loop. Without an external source of energy, shoes cannot create extra energy for the runner.
So if the spring returns more energy, it also requires the runner to produce more energy.
It's not necessarily energy return as the big brands (mostly Adidas) claim, as much as it is reduced energy loss. The Boost doesn't "return" any energy, the runner just loses less energy.
I think there is a video on YouTube where an Adidas exec. talks about the science behind Boost.