I go along with some of the other folks. Oil pressure and voltage gauge. Oil pressure can warn you of a leak before engine damage occurs. Otherwise, you just have the warning light, and sometimes you already HAVE damage by the time it comes on. I agree that the water temp gauge in these Nissans works just fine. No need to switch it over to an outside gauge.
One cute gauge to have is an intake manifold vacuum indicator gauge. Back in dinosaur days, I had a 66 Impala SS with a factory vacuum gauge almost the size of the speedometer. It was way cool. Found a picture of one. Brings back memories. I think the purpose is to show you how you can increase your gas mileage by keeping it in a certain range or something. Pfft. I paid no attention to that. Gas was like 45 cents a gallon back then. You handed the guy a ten dollar bill and you got back change. One time though...I forgot I had studded snow tires still going and my brother told me to dump the clutch and do a big burnoff. So I revved it to about 4000 and dumped the clutch. The studs caught the pavement, and one of the motor mounts broke. Engine banged into the hood. Only damage was slight dent to the air cleaner, but I sure felt foolish.
