You know, in the last few days I decided to pick up New Vegas for another run, this time with an energy-weapons only character (on very hard though) and it's rather impossible 'til the middle game: ammo are rare just like parts. And while it's true that are meant to be rarer they don't really give you any advantage over regular ranges weapons: even in the late game there are equivalents that are just as strong in the firearms category, despite the shortcomings of Energy weapons in the first phase of the game.