1. No they're not. They share less than the Fairmont and Fox Mustang or the Falcon with the classic Mustang. They share bulbs, a few brake parts, and engine mechanicals (except the 2.0 (Pinto only) and 302 (Mustang II only).
2. Beauty is in the eye of the beholder... or the beer-holder. I personally think all of the foxes except the fox Capri, 85-86 fox Mustang, and fox T-bird TC are ugly.
3. That's been disproven by people smarter than you or I.
http://www.pointoflaw.com/articles/The_Myth_of_the_Ford_Pinto_Case.pdf They didn't blow up any more or less often than anything else in their class.
4. Pintos (and Mustang IIs) are very light, 74+ models have great front suspensions, and anything you can do to the 302 in any other car can be done to the 302 in a II. I used to spend a lot of time "in Mexico" beating up on a lot of high-dollar cars in a wrecked II I saved from the scrapyard, gutted the interior, built the engine and trans, and went looking for a fight back in my younger and dumber days. It won a lot more than it lost. That particular car was already twisted from the wreck when I bought it, I got a lot of good years out of it, and when I was done, I yanked the powertrain (2/3 of which is now in my dad's Capri) and threw the car away.
Again, boring. Same arguments I've heard for 16 years, and not even the good ones.
Real reasons I prefer a II over a fox?
1. Lighter
2. That front
suspension (no bump steer, smooth as glass, and no strut towers)
3. I like the challenge of fabricating or hunting for what I need vs. buying off the shelf
4. Nobody expects The Spanish Inquisition... err... Mustang II! (Seriously, I love the extra butthurt expressed by the haters when it wins.)
5. Big deal, it's a II. I love the things, they're cheap fun, I dig most of the looks (hate the taillights and the stock 13" wheels, WTF was Iacocca drinking?), but if something happens to it tomorrow? Big deal, yank the powertrain, find another one on Craigslist or Ebay for next to nothing, and do it again. Barring theft or fire, not a whole lot to worry about.
Wanna go back to drooling over the Ford Nien Numb... err... GT? (I actually think everything about the new GT is gorgeous except that grille, kind of like the 2013+ Hyundai Genesis Coupe, it also looks amazing from behind and the sides, then you get to the front and it's like... eww...
).