it would be. It's true you don't need it because of the presence of the synchros, but it does save wear and tear on the synchros since you're not really engaging them when you double-clutch. I double-clutch my Z and did so with my RX-7 as well. I didn't do it for any particular wear benefit but rather because it was an ingrained habit from shifting formula fords with gearboxes that had no synchros.