I'm not 100% convinced. I think it's hard to get really smart people to work on problems that aren't interesting. Asking a team to make food preservation 10% better won't invite the creativity and determination that asking them to preserve food to Mars would.

I think, when you take humans into account, you're better off setting interesting and challenging goals, with many useful byproducts.

That is the best argument for "spinoffs" that I've heard. Well done.

I still think it's pretty weak though; the inspiration benefit seems unlikely to overcome the lost efficiency, in general. And different people find different problems inspiring; some people can be inspired by practical problems (e.g. "how can we lighten the backpacks of trampers").

Do you (always?) realise that need before the product is made?

Are you suggesting these spin-offs are (always?) after-the-fact justifications using issues that were not pressing concerns?

The problem with attempting to justify space exploration with spin-off examples like food preservation is that it risks provoking a 'so what?' response. Piling on unimpressive claims does not strengthen one's argument, it dilutes it, and gives the opposition an easy target to dispute.

When Clarke came up with the idea of communications satellites, he, and others, thought he had come up with a before-the-fact justification for space travel, as he expected these relays would need regular maintenance, but another claimed-spinoff-but-not-really, semiconductor electronics, obviated the need.