I hear what you are saying, but I think you would find that the benefit of this type of work, dollar for dollar, is well beyond just the science that might be revealed, and much more valuable than the dollar for dollar benefit of much more costly programs.
One of the purposes of NASA, not expressed often enough, is to help foster and maintain a sufficiently educated workforce so that the national (defense) needs of our nation are never in peril. The manned and unmanned programs (and some people like one over the other) both inspire young people towards engineering disciplines, maintain critical industries that are able to produce dual use technologies that otherwise could not be sustained, and push new technologies that flow back to shape our future and make our lives easier (for better or worse).
Infrastructure certainly needs revamping, but the tech for new roads and bridges is always going to be there or able to be reconstituted in days or weeks, as opposed to years to restart some high tech manufacturing lines. And the savings available from other wasteful govt redistribution programs far exceed NASA's total budget.
Thank you for the thoughtful and cogent reply.