Tell me: what exactly would have been worse if the US had never had a manned space program? The whole thing feels like a vanity project, not something that delivered value. It could all have been delayed while launchers got cheaper without loss, as far as I can tell.
Polyimides like kapton are a good example.
Polyimides date back to 1902, but you couldn't buy anything like kapton tape before the space programs created a need for such materials and capital to build out plant for them.
To make a valid spinoff argument, you have to show that the particular technology would not have come about without NASA. That sort of contrafactual, alt-history argument is really hard to do. It's why alt history has such a bad name in history circles -- you can't really show anything. This means all spinoff claims are dubious. Not only are they presented without the necessary evidence, it's difficult to see how the evidence ever could be acquired.