Having a good ground is imperative. most electrical power leakks aren't due to the power side of the circuit, but rather not having a good earth. This is no more important than in the stereo as it eliminates both system noise and ignition.
But getting back to the topic of stereo installations, I thought you guys might like to have a look at what I've just finished in my '78 120Y. I'd be interested to see people's thoughts. Maybe it will also give someone else inspiration for their own system: