Military spending in WWII led to the invention or development of (to name a few) penicillin, radio navigation, synthetic oil and rubber, jet engines, nuclear power and computers. However some of these were pretty close to being invented even before the war, so it's hard to say how much the war progressed technology.

> However some of these were pretty close to being invented even before the war

Penicillin, for one, was discovered over a decade prior to WWII. A method of mass production was developed in 1940, but have no idea how much that had to do with the war.

> Which seems to imply that military spending is pretty beneficial for humanity as long as it's spent on researching new cool ways of killing each other, and not on actually using them.

The sixties-era DARPA method: throw a bunch of defense money at a bunch of really smart people without getting too specific about how much of the research should proceed.

Exactly what I had in mind.