I think there's something to be said about being more aero - but only if it's a big change, like going from the high and wide simulated braking parachute position of many hybrids/mountain bikes to a narrower, more stretched out and lower road bike position. The little changes from one road bike to another might not matter as much.
You can really tell the difference when riding in a head wind. All else being equal, the road bike rider can generally go faster for the same effort.
I think that narrower, harder tires make a big difference too, but by the time you are down to 23-25 mm, not much more can be gained.
V-section rims, I'm not too sure about. I find that even a relatively mild V really catches the wind sideways like a sail. I would prefer a more conventional rim if not racing.
But as far as weight goes, unless it's a lot, it won't make any difference. You can spend very big bucks and end up saving less weight than that of a water bottle. A full water bottle is about a litre, so, it weighs about a kilogram. What's shaving a few grams here and there going to do? So, the moral of the story is that if you really want to save weight, I guess you have to ride with a team car behind you to carry the water.