The main thing of space exploration (outside of missiles and satellite com or other military applications -- which was NOT done by NASA) was development of integrated circuits.
But as for "the rate of return" -- high energy physics probably did much more for less money invested -- accelerators and detectors for medical applications, superfast computing for pretty much everything and, of course, World Wide Web (browsers and such). And that's besides the main goal -- studies of particles and their interactions.
No one argues that space is "the final frontier". But many things there could now be done with robots and do not require expensive human participation.
What kind of medicine was developed in weightless environment (and requires that environment)?