A lot of things went into my decision. I just had my first kid, so that 3rd door with the VN was a huge plus. Also my Mustang had just shy of 60k miles so I was out of warranty very soon. Lots of maintenance coming up that was going to cost a decent amount (spark plugs, new tires, brakes, etc..)
The VN just made too much sense to me. I added a door for the kid seat, I gained a 10yr/100k warranty, I reset all the maintenance, tires are much cheaper (285s on all 4 w/ with the Mustang)
Also living in CT, RWD 400+ HP is not the easiest daily driver for winter.
Oh and 11 mpg upgraded to 20+ on a regular basis.
Again, it just made too much sense for me. I will say, that so far I am not regretting my decision. Yes there are definitely things I miss, but the VN is such a capable car and so much fun to drive. I love the fact that I can confidently throw it around corners. I can find the limits on the street with the VN and with the Mustang all I could really do is accelerate in a straight line at a light or on the highway. Which don't get me wrong, I loved! A very different car, but still just as much fun!