Can a hypothesis that has been rejected be of any value to scientists? Why or why not?
Yes, it can.
One famous example is the Michelson-Morley 1887 experiment to determine the so-called aether-drag, that would influence the speed of light, when measured in different directions. See: https://en.wikipedia.org/wiki/Speed_of_light#.22Luminiferous_aether.22
The failure of this experiment completely disproved the concept of the "lumiferous aether" and established another cornerstone for the theory of relativity.