This is where I think lighter weight for a given aero performance can make a difference in road riding and racing, and probably more in crit racing.
Once the race has taken shape, and most people are at their limits, there is a lot of testing your competitors going on with little accelerations and trying to gap your opponents to shake them out of your slipstream. Alternatively, you're on the rivet trying not to be gapped. On crit courses, there's the accordion effect coming into and out of corners, where you have to slow down, corner hard, and accelerate quickly again.
Anything that reduces rotating mass, helps put power to the ground better, and allows you to accelerate more quickly to make it easier to stay on the wheel in front, or help stop you losing the wheel in front in those surges, is going to have a disproportionately high payoff compared to the difference it would make riding at a steady state, in a wind tunnel, or riding alone, whether or not hills were involved.
The cheapest way to maximise this effect is to buy lighter tyres!