I didn't think much of mine either until I followed a buddy with one, I now only have mine on when it's some combination of foggy/rainy/night, which happens a lot up here in Washington! If I were the OP, I'd go the switch option so you can have the fog light independant of the normal lights. The Z-Store has a nice OEM style switch that goes by the cup holder but it's very pricey and does involve tearing the interior out to route it, sounds daunting but once you've done it once it really isn't that hard.
The Z Store! Nissan-Datsun 240Z-260Z-280Z-280ZX-300ZX(Z31/Z32)-350Z-370Z Parts: Rear Fog Light Harness & Illuminated Switch, 09-10 370Z