I don't think Maps in iOS 6 will be the biggest selling point. At least, I hope not. If Apple can bring is close to being on par to Google Maps for Android, then I think most people will be satisfied. What is great about Google Maps for Android isn't 3D (it doesn't exist yet and I doubt many people care). It's the integration with places/reviews along with voice guided navigation. Apple may wow people with 3D maps but at the end of the day, they need to create a feature complete maps solution not just some pretty maps.
If Apple released iOS 6 with a free, high quality map application, that allows downloading maps beforehand (for example for a town, or for a journey with plenty of space for detours) and that allows turn-by-turn navigation, that would be quite a selling point. I want to replace my Tom Tom, because both the hardware and the software are just rubbish, so that cost would be subtracted from the cost of an iPhone or iPad, making it a lot cheaper.
(Turn-by-turn software taking advantage of the compass would be great. One problem with Tom Tom is that as you start a journey, it doesn't know which direction you are pointing, so quite often the first turn is a guess with a 50/50 chance of getting it right. )