The one thing you haven't indicated is the amount of time you have over there. If there's space \ time in the schedule, Another Disney day is never going to hurt, especially if it happens to be a busy day\days in the park.
I definitely agree with picking the highlights to make sure you get them done, but I also recommend picking your path at Disney and working your way around, rather than hopping your way from one side to another. I can't remember the detail, but a study was done that suggested when everyone reaches the hub they naturally gravitate in one direction - I recommend going the other way (i wish i could remember which way it was, but i'm sure someone here remembers!). There's plenty of planners, guides, hints and tips, so best thing to do is have a google, and see which seems a best fit for you.
Understanding your preference for lower thrill attractions, Magic Mountain probably isn't worth the hike, however, don't ignore some of the other parks (Like Knott's for example) if you have the time in your schedule.
While you can watch fireworks from many hotels, +1 for catching it on main street \ the hub.
+1 Don't miss Fantasmic if it's operating, paint the night is also pretty cool, and world of color if it's back up by then.
With an 11 year old, there may the the eye-roll that some things are too childish - especially in fantasyland. By all means ignore the fantasyland flats if a carousel or dumbo is too 'kiddy' for you (they're still good though) but don't walk past the fantasyland dark rides - even if you only do them once. Toontown is still worth a look as well. Everything in Disney is suitable for all (most) ages, so unless you can see the full experience and make a call then, give it a try - at least once if you can.
Enjoy!