Well, I highly doubt that the kind of rockets they are developing for Lunar and Mars missions will be mich better, if any better at all, than current ballistic missiles armies around the world already have. Those space rockets are huge and meant to more or less safely carry people over a long distance in space. Warheads are meant to carry explosives while also being hard to detect or stop. I'm no rocket scientist, but I believe that huge space rockets would defeat the purpose, as they would consume a lot of fuel for nothing, while also being much easier to spot and stopped by shooting something at them.

So I think the opposite: we are way past the point of space exploration being directly useful for weapons.