Mine is a Gen1 - an i170 - but I did the conversion to XT and then put some nice looking wheels and tires on it. It is faster because the diameter of the tire is larger than the stock i170 tire and even a tiny bit larger than the stock XT. My neighbor is a CHP and he hit me with radar one day and said I was doing 18. I said all you cops are alike - I couldn't have been going any faster than... 17.
As much as I like the fatties, I usually only use them for car shows and other extended outdoor events. I use my seg for a mobility aide, so I am indoors a lot. I found some great motorcycle tires that fit the stock rims and the overall diameter is 21", so I'm still going 17 top speed... or 18 maybe. Can't mount the fenders over the motorcycle tires though.
Les Schwab mounts all my wheels and tires and will check my air regularly. They have been very generous in their pricing too, but they can't supply the actual tires or wheels - those are ATV or motorcycle items. I think you're way off at $800.00 though. I know the Segway gear is pricey, but ATV or motorcycle wheels and tires ain't. I think the most I've paid for a single tire is about 80 bucks and the wheels are about that too, or less. I think the XT hubs were only about 60. I don't remember what the bars and fenders were, but I don't use them anymore anyway. I get a little dirty in the rain or wet weather, but it's really nothing compared to how dirty you can get in a lot of other sports and activities.
Jim