Yes, pedal weight is worth it. It’s not really a zero-sum operation, because there are always losses in any system, so you will always pay some price for lifting a heavier object that you won’t get returned on the way down.
There have been some demonstrations that have shown that pedal weight is one of the few places where weight actually makes a really meaningful difference, even much more than wheels, but I haven’t seen enough of the data underpinning them to call them “studies” or to attest to their validity.
But certainly, there is no downside to a lighter pedal (which CAN include other upgrades as well), and there MAY be really meaningful benefits (on the order of magnitude of a few watts).
Pedal weight, like most rotating mass, gets played up as being really important, but it’s important to remember that unlike with wheels, the aerodynamics of a pedal don’t change much with weight; it’s not like a shallow section climbing wheel vs. a deep section aero wheel where aero way trumps weight. In this case, it’s ONLY weight.
There might be a savings of a few watts by switching to a more aerodynamic cleat/pedal (ref: http://www.speedplay.com/index.cfm?fuseaction=home.slipperypedals), but it’s hard to see how reduction of such a small amount of mass alone could get several watts of savings.
The increase in rotational inertia is only an issue during accel/decel, and then only when there is desired deceleration (ex. stopping pedaling ahead of a sharp corner). The energy savings from faster reaccel of angular velocity is so small and intermittent, the average is <<1W. The “it’s rotating weight” concept doesn’t seem to have much actual impact.
That all being said, pedals are not a bad place to shave weight from a bike from a $/g perspective (until you get to extremes like the uber-expensive Speedplay Nanogram pedals), coupled with the fact that you rarely give up functionality in pedal s when shaving weight.
