I get the feeling his "vision" was just a load of crap he used to justify his actions.
Add another one who has that opinion.
As for the NCR, I believe failing or succeeding in taking the Mojave area would have giant long term consequences.
Annexing the Strip with it's incredible income and point of trade, could mean a huge boost to them as a nation financially. They seemed to be have begun creating sources of industry in the area in fields of construction, as well as scientific research and agriculture. Not to mention the giant water resource of Lake Mead, which they seem to now base their currency upon, and see it as a resource worthy enough to base it's value upon. It's ready supply coupled with it's distance could possibly average out to preserve the value of their money.
Could be the fuel for an explosion in agricultural output. It's water also seems to be the Legion's resource-minded interest in the region as well. Water must be a major point of holding power in the time period of the fallout universe, all the consideration toward it taking in mind.
Most importantly of all, there's the Dam. The electricity generation seems to be the only real reason they're so heavily interested in the area. Losing that would be a giant blow to their continuing social and economic progress.