I agree with your beliefs on why so many have ended up failing. I also think there is a problem with organization and time too.
For my part, I keep trying to do something, but after I get home from writing code all day, the last thing I get inspired to do is look at an IDE
I think Jirka has the right basic idea with TatraApp and QCar. A basic shell that supports plug-ins and then offer some basic plug-ins to get it started.
For me, the only thing I really care about is Music. A good simple Music player is all I need/want (so early versions of AMP still works fine for me, but i'd like something cleaner (no offense Bobby) with less stuff that I don't need/want running around).
But I would like it to be extensible so that if I ever get off my *** and get a 2140 (now that we know the protocol) or do some of the projects I keep talking about, I can integrate them into the App without a lot of hacking or code rewriting.