Hi Node-0, welcome to the forum and great first post.
I remember the first time I wrote a for loop with pwm control and was able to dictate to a fan exactly how fast to turn
and when to speed up or slow down...
There's something great about controlling physical devices, I like programming fancy GUIs as well but you don't get get the same thrill as watching a mechanical device move because your code told it to.
ah the misery of circuit design, may it fade away
For me the hardware design is one of the best parts, but not the building and debugging. I hate that.
For people making their own shields/hardware the 3v3/5v thing doesn't matter much, it's just the 500 existing shields that may be orphaned. But then it's probably fair to say that the Due is for more advanced users, the mainstream will still be the smaller 5v Arduinos.
the 'shield' moniker is not an accidental nomenclature, I have a suspicion that the very word is rife with meaning as it
applies to electronics...Here is a piece of equipment that will 'shield' the user from the details of the electronic circuit.
Who knows. Personally I think it's just a stupid name to match the stupid shape. All done to appeal to artists. That said "shield" is a lot easier to say than "mezzanine board" or "daughter board".
My predominant hope with the Due is speed, sheer speed of calculation and a ton of inputs and outputs, I tend to like sensors, LOTS of sensors.
That shouldn't be a problem.
Someone mentioned realtime spectrum analysis, yeah that sounds interesting too.
I see the Raspberry Pi as an awesome secondary processing node for the primary sensor data acquirable with the lower level MCUs...
Yep, sensing and low-level data-dicking with the Due, then offload the fancy GUI display to an RPi or some such.
Anyway, that's my two cents...
More like $2 
Rob