exactly...

My #1 concern is the audio quality. Based on what I've read so far, I assume the 30-pin connector offer the best line level output. Will know when my cable arrives tomorrow.
Thanks to all!
The thing to note is as above: the RCA-in on the stereo end, as this too is analog, just as the headphone-out on the iPod is. Hence, you won't achieve any better sound quality using the 30-pin over the headphone-out.
What you need is a car stereo that has a 30-pin (or Lightning, for newer device users) DIRECTLY GOING IN to the stereo without a separate connection on it. This not only will achieve the "line level" better quality you want, but should also offer you additional controls directly on the stereo itself.
Ultimately though, does it matter? When you're listening in a car environment, you have so much background noise (engine, street, etc.) that the difference is likely pointless to you.
Oh, and don't forget to make sure you're running your car's engine, as otherwise you'll run the battery down – like I did a while ago, having to call the AA out to start me up as the battery voltage had dropped below the minimum level needed for my car, before immediately taking the car for a good half-hour run to top the battery back up from the car's alternator!