I think the item balance based on distance is a better design than in previous games where the front runner has a triple banana and you just get an occasional red shell and mostly bananas, green shells, and sometimes Mushrooms? I kinda like getting triple reds when I'm far behind as it'll give me a fighting chance to actually catch up. Same thing for the Super Star. I know it's generally not cool to be first and second has triple reds since you'll probably get hit at least once, but first is a really advantageous position since you don't have people in front of you laying hazards compared to 2nd where you have to deal with behind AND in front.
I like twelve racers per track too. I like the mods in Mario Kart Wii that increase to a whopping 24 racers. It seems super crazy.
Finally yeah I think a lot of these are fair. Winged Spiny Shell does suck and is nowhere near devastating (and hella useful) the Spiny Shell in Mario Kart 64 was. I also think it sucks to race Staff Ghosts for unlocked content most of the time.
Also, I forget, but I still remember Mario Kart Wii not having GP for 2+ players and that *sucked* because at the time this means one of us had to sit out to unlock the roster. They at least fixed it in Mario Kart 8.
I feel red shells in MK8 and perhaps 7 (though I'm not sure) ignoring flyoff glider ramps and the like makes them far more annoying than the blue shell