I personally think diesel is way overkill for your needs. If your towing as infrequently as you claim, the price is darn near impossible to justify. Gasoline has come down in price pretty substantially and that alone should be reason to look at a gassser. While everyone likes to tout the EB as a game changer, there is an old saying that "there is no replacement for displacement". An engine that loafs along will last much longer than an engine tuned to the edge and ran hard. I would agree with the general feeling that a 3/4 is a much more capable truck and will handle your current load nicely. If you upgrade/find a good deal on a gooseneck, you will already be set-up for that step. The other thing to consider is (depending on your # of implements) you can also load the bed of the truck up and not be white knuckle driving. All it takes is one near death experience to change your perspective on what matters. If ride quality is of concern, the new RAM HD trucks are coming out with an air ride suspension option in the 2500 and up trucks starting in '14.
If you're sold on the EB and a 1/2 ton, spec it out as heavy as possible, keep an eye on your GCWR. You might be surprised at how quickly different options reduce your capacities. I would think that as long as you're close to your weights, a good W/D hitch will greatly help things out. You can also add some firestone ride rite air bags if you're truly occasionally towing your heaviest load.
It all comes down to what your willing to spend, what your acceptable level of risk is, and if your going to let someone else drive your vehicle.