https://en.m.wikipedia.org/wiki/Strategic_Defense_Initiative
I wouldn't say that nothing useful was gained. It appears to have furthered our sensor technology quite a bit. True, it was never going to work as intended, but Reagan didn't know that. This is the same guy that was terrified by the film WarGames, so of course he wanted the SDI program. He was a shitty president for many reasons, I wouldn't say that SDI was one of them.