Out of 46 bikes I have owned, and several more I have ridden, the Vulcan 750 comes in a close second to the 1500 Goldwing comfortwise. The reason for it's amazing comfort, especially for a 750, is mostly due to it's ergonomics. The seat/bar/peg relationship is perfect. The stock seat is also extremely comfortable. If you install a riders backrest, or strap a sleeping bag to the passenger part of the seat to lean back against, it is like riding an easy chair down the road. It is a completely natural sitting position, much like sitting in a luxury car (or a recumbent bicycle) with your feet out in front of you, leaning slightly rearward with good back support, a wide seat that is not to hard and not too soft, and bars at the perfect height and perfect pullback, so you don't have to lean forward to reach them. Your arms are completely relaxed, with a bend in your elbow. It is nearly an effortless ride, with no pressure points anywhere.
There is a reason why Kawasaki sold the Vulcan 750 for 23 straight years completely unchanged except for paint. As someone who has put 160,000 miles on them, I know what it is. Many others also know. Other than possibly the Virago, there is simply no other 750 size bike that is this comfortable. The Vulcan has the advantage of a lot more power than the Virago, and hydraulic valves, but the Virago has plenty of power for touring, the simplicity of air cooling, and easy to adjust valves. You really can't go wrong with either one. Sadly, neither one is made anymore. Just like the 1500 Goldwing, they were replaced with something less comfortable.
2002 Vulcan 750, 2001 XT225
2008 Vino 125, 2009 Genuine Stella
2012 Zuma 125, 1980 Puch Newport moped