Actually... we continue to gain high-quality scientific data from probes and robotic missions that operate in environments impossible for humans to endure. Robotic explorers do not require sleep, food, oxygen, or the complex, heavy life-support systems needed to protect humans from radiation and extreme weather. Consequently, our current rovers have provided consistent, long-term observations that no human team could match in terms of duration or scope.
We do not need to send people, philosophers or poets into space just so they can provide personal testimony of the "wonders of the universe." That awe and wonder can be experienced by anyone from Earth through the high-resolution imagery and scientific data streaming back to us.
Sending humans to Mars (or to the moon) is an incredibly expensive and resource-intensive endeavor. A single human mission would be significantly shorter, exponentially riskier, and would cost orders of magnitude more than a fleet of robotic missions. When we evaluate the scientific return on investment, robotic exploration remains a far more efficient trade-off.
"The Overview Effect" is an interesting psychological phenomenon, but it is an internal, subjective experience for the individual astronaut. While I do not doubt the sincerity of their feelings... such a thing is simply a personal benefit, not a scientific justification for the massive expenditure required to put humans on Mars.
We should not fund multi-billion-dollar interplanetary missions based on the hope of providing a romanticized transformative psychological experience for a handful of individuals, especially when the same 'perspective' on the fragility of our planet can be (and has been!) achieved by those who have never left Earth, simply by engaging with the imagery and data provided by our robotic missions.
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