In reverse order:
3. Unhiding the Library is easy as falling off a log.
1. Use whatever method you want to show the Library; "Go to..." menu, a Finder sunstitute (good to have, anyway), etc.
2. Drag it to a Finder window sidebar.
3. There is no step 3.
2. ML has a "Save as..." it still uses the same built-in functions, but the choice is there in the File menu.
3. Your trouble with core-audio is not world-wide. Some have it, others don't. I have never seen it but I'm not into heavy audio use, just a twice weekly audio editing/disc burning routine. Have you searched for the occurrence of the problem in ML?
Almost every one will have a problem with one OS or another. Most of us just move on and make use of the new features. I don't like the 'fifty-shades-of-grey' either, but colors show everywhere else in Finder windows.

And, at least in the "Devices," "Recent Documents" and "Shared" items in Path Finder (which also throws in a Terminal window automagically if you want one!

I've also used Lion Tweaks, as well as Mountain Lion Tweaks for that, but, as you say, it has to be run at each restart... maybe an AppleScript?

I'm especially happy with the Auto Save function because my wife has refused to grasp the concept, many decades old, of saving often and religiously! Time Machine also helps there, of course.
I'm not sure there are too many drivers required by the new hardware, except, obviously, the Retina MBPs. But a thorough search might bring you some favorable news.

Actually, what I miss most are the double-arrows (usually only available via third-party utilities) at the end of scroll bars...