The funny thing is that almost all the really earth-shaking developments in engineering and technology usually originated with some basic research in science with "no practical value". Studying stellar evolution leading to the discovery of fusion comes immediately to mind.

Appllied research rarely makes any fundamental breakthroughs, and when it does, they are usually by accident, in an area totally removed from the original area of research.

"...the fact that we still know so little about it could mean there
is something unexpected out there that might affect all future
such probes, or perhaps there is a phenomenon or set of objects
that could provide benefits to future humanity we cannot even
conceive of right now - even though part of me reviles at the
arrogant idea that everything in existence is supposed to benefit
us in some way."

That is one of the most eloquent arguments I've heard yet against the commodification of scientific knowledge. Private enterprise is very good at applied research, but not so good at basic research. The exception is when private enterprise funds basic research as part of a philanthropic
effort. An enlightened busunessman is usually more perceptive than a government bureaucrat about where the money will do the most good, providing they are under no pressure to please the stockholders.

From my own field, I recocognize the enormous impact the industrial philanthropists of 19th and 20th century America had on American astrophysics. And they did it with no profit motive expected, but purely as a social benefit to the community. Perhaps small and cheap privately funded space missions could serve the philanthropic purposes of the 21st century the way the big privately funded relectors served astronomy a century ago.

I thoroughly agree with your "many cheap probes strategy" of space exploration. Space is big, and it's the only way we're going to survey enough of it fast enough to actually find something which will justify a full-bore manned colonization effort. When you're randomly shooting into the dark, a shotgun will hit its target faster than a howitzer.