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On a stock car, probably not. On a bolt-on or FI car, then yes. The lighter rotating mass makes a difference on the longevity of transmission and rear end parts.
Technically, it does cut down on rotational mass, and will yield some gain. Whether or not you notice it, or your time slip reflects it, there is some gain. No way around it, Whether or not its worth it or not is up to you man. $270 isn't that bad for a good aluminum DS. They want $700 for an S197 DS!