Drink@Drink - Depends on what you're trying to do. For chasing noise, there is little better than an oscilloscope. For trying to troubleshoot a circuit involving audio, there is little better than an oscilloscope. If you have super-expensive speakers you are about to hook up to your homebuilt amp, maybe putting a scope on the outputs first would be a good idea.
@ViperGeek is correct, though. If you want to truly "tune" audio equipment to ensure you have equal response across the audible range you may need a spectrum analyzer. That said, in my experience car audio is less about accuracy and more about "does it work, and how can I make it work louder/with more bass" - for which role this scope may fit the bill.
DrinkIf you want to set your gains on your amps and find out at what volume level your head unit begins to clip then an oscilloscope will do that just fine. A set of test tones will also be needed.