" Manned mission cost many orders of magnitude more than unmanned while delivering a tiny fraction of the science of unmanned missions"
Manned mission can do huge amount of science that robotic missions can not, and they have a wider scope of capabilities.
Yes, send rovers, send robots, but send people was well. The benefits in RnD, hope, excitement, and the ability to just grab a shovel and find something interesting should not be underestimated.
If people aren't excited about spaceflight, then eventually even the robotic mission will be cancelled.
A human could literally car a robot somewhere they they observed to be interesting, let it go do it's thing in that area.