Like many of the above, I purchased a new 2500 HD and really wished I would have gotten the 3500 HD. My 2500 HD does not have the rated capacities to haul many of the fifth wheels on the market today.
I will always buy 4WD whether I need it or not. To me, it is just like buying insurance in that it is a great thing to have if you find yourself in a situation where you need it.
I would not buy a new 2015/2016 Super Duty at this time with the all new 2017's coming out within the next year. The new 2017 Super Dutys are going to have a much stronger chassis and numerous safety & convenience features that are worth waiting for IMO.
I'd find a way to wait for the 2017, even if it meant buying a used truck to get you through the next 10-12 months. If you found a decent deal on a used truck, you could probably drive it for a year and sell it for what you paid for it.