Grand socio-economic projects aren't really my couriers style, but there is one very important thing he wants to do for the Mojave: Wipe out that [censored] Legion.
If given unlimited power this would involve the creation of vast border defenses along the natural boundries of Vegas. Ideally run with as much automation as possible to reduce the manpower cost that can be better put into actually improving the region rather than keeping the crimsons away. Taking the fight to the Legion is a possibility, since they can always march in a direction that is not west across the colorado. However, this would require some sort of occupation government for the new lands that Vegas would acquire, which my Courier doesnt really want to ever deal with or think about, being a statesman is not his job, although I do certainly have my own ideas about what would be best for Vegas.
Aside from that, providing the residents of the Mojave with weapons training and the means to defend themselves would go a long way. A lot of people in the western-ish half of the Mojave are using very underpowered weapons. I think this is more do to gameplay and story segregation, but if we take it at face value then a good trading agreement with the Gun Runners would give the locals the means to defend themselves against the dangers of the wastes aswell as any foriegn incursions.
My Courier believes in self-determination and indvidualism, and would rather give the peoples of the Mojave the means to further their own ends. This is not a perfect set of values, since as I said in the last paragraph with his infinite power he could turn the Mojave into a special kind of hell seperate from the Legion, where everyone is highly armed and quick to resort to weapons. It depends on the character of the people involved, and the Mojave is a giant mixed bag in every way.