1000 unmanned missions will learn more, and advance technology farther than will one manned mission with a 50% probability of failure/tragedy.
Even if that is true, and humans have a greater potential to find and adapt the unexpected, the absence of humans in the space program deprives it of anything symbolic and to which the masses may be able to relate. It will be even easier to cancel the space program and simply pour the funding into the endless pit of social services and entitlements IMO.
A thousand robotic missions will not deploy a system capable of noticing something unusual or out of place - perhaps something the size of a dime on the sidewalk - picking it up, looking it over, and finding something unexpected all within ten seconds of mission time.
A thousand robotic missions might learn more than one manned mission, but they probably wouldn't learn more than two manned missions.