I don't own one. I did have a similar engine in my Multistrada and they are great engines. They are much better than just a few years ago in so far as the response from the throttle is much better than the 80+hp at the wheel would suggest.
The riding position is not good if you choose to do High speeds for long times, especially if your tall. The wind becomes tiresome from the lack of a screen. I would look at what you intend to do wih the bike.
It is really a retro bike with todays performance. A lot of people get them then discover there are shortcomings. The performance of the bike is much greater than the design intended in the 70's. Even in the 70's people who were doing lots of Highway work fitted screens to their bikes. The joke back then was that you were commiting Blasphamy if you fitted a bikini fairing to your Darmah (the darmah is much like the style of the GT).
As far as the service side of things go. The belts seem longer than in the early nineties so anyone can fit them. The fuel injection and valve clearances do not need doing as often. Having said that the reason is Ducati is allowing greater tolerances in the services than when it leaves the factory. That means the bike does not run as crisp when its getting close to a service. It's best to get a Ducati shop to service the bike as they may need to reset the computer.