I've owned my 2005 VTX1800S for 22 months now and put 31,000 pleasurable miles on it. My first time on a VTX1800 was in the fall of 2009 and I didn't get off until 100 miles later. At the time of this ride, I had not been on a bike of any kind in 5 years. The last bike that I had ridden was a Kawasaki Concours in 2004. I was immediately sold on the VTX1800 having never ridden the VTX1300 for comparison. Less than a year after purchasing the VTX1800, I also bought a VTX1300, both the same year models and color. The stock seats and exhausts had already been removed from both bikes at the time of purchase. Mustangs on the 1800 and X Extremes on the 1300. Cobra pipes on the 1800 and Vance & Hines on the 1300. Both bikes came with a Pro-R hypercharger and Cobra Fi fuel processors. There IS a significant difference between the two bikes. Depending on my riding mood, if I wanted a fun cruise on curvy two-lane roads and highways, the 1300 was the choice. For serious, no non-sense Interstate and Freeway cruising, the 1800 gets my vote. The 1300 is well suited in both scenarios of course, but being a pilot and addicted to torque, the 1800 is the one that gets the adrenaline flowing. In short, the 1300 seems to be the perfect 'all purpose' motorcycle and the best thing for the 1800 is to find the shortest distance to the Interstate Highways.
The 1300 has significantly better fuel economy when compared to the 1800. You can expect to get the same fuel consumption out of the 1800 as you would an automobile with a V-6 engine. New V-6's get better MPG's than the 1800.
My VTX1800 has been extremely 'low maintenance', oil changes every 4,000 miles and tires when needed and that's IT. I learned that my style of aggressive take-offs will eat up a rear tire on the 1800 real fast. I barely got 3,000 miles out of my first new Dunlop on the rear. I can be a little easier on 1st. and 2nd. gears to keep from having to set up a savings fund for a new rear tire every 4 to 6 months. I've also added just about every Kuryakyn, Show Chrome, and Cobra accessory available and the installation of all the these parts was a breeze. So far, I would not give up either of my VTX's for any other metric or Harley cruiser on the market. The styling of the VTX is unmatched without question.
All Kuryakyn, Cobra, and Show Chrome accessories, just name one.