A pretty good list, IMO, although perhaps a bit drastic or unrealistic as rasmusbr points out. Instead of removing all crap applications (your #1), move them to the "Junk" category then have a default hide for the category. That allows the teenagers to have their stupid apps -- and they can feel even cooler by having to go in and enable the category -- while not bothering the rest of the user base.
I suppose one way of addressing #2 (duplicating stock apps) would be to have another (hidden by default) category. That way someone who wanted a replacement music player could get one without forcing everyone to slog through garbage apps.
And while #4 (eliminating in app purchases) is important as it cuts to the core of some problems, it simply isn't realistic. Originally, Apple did not have them. They were added to appease large developers. Not going to happen, but it would help if it did.
Even though rasmusbr is correct about what will happen with #6 (time limited 100% refund policy), without in-app purchases the model would not be particularly successful.