Okay, I can see this. I know that a fair number of resources are extraordinarily rare on earth but space bodies are often almost exclusively made of - iridium for example). My knowledge beyond that is limited, I don't know how much those resources are worth, or if there are future uses for them we haven't discovered because of current cost barriers due to rarity.

I'd say though, lets pretend that an entire "flight" to intercept an comet/asteroid/material-rich-spacebody (Sorry I don't know the technical terms here) could be reduced to 100million USD. That material would have to be worth that 100million USD, not to mention all of the R/D.

Again personally I want humans to one day achieve it just for the heck of it - why not? But others are money driven and I'm not sure it makes actual financial sense (in terms of money making)