My 2c worth
When I fist started thinking about an outfit, I asked all the usual questions and when it came to bike choice, it came down to the two; K1100 and GSX 1400. The k1100 became available first so that was what I built. Two and a half years later I've now bought a 1400 and the work has started on that.
The BMW was almost trouble free (except for a broken tailshaft, which ended a trip, and a broken exhaust header, which didn't.) over varied roads, from mediocre to poor dirt, to a few highway trips. So it's now going to be interesting to see if the 1400 gives me the same service.
I've made the change mainly to go to a later bike (from a 92 BMW to a 2003 1400) and as someone else has said, a chain and sprockets are easier to carry than a diff. The extra power can't be a bad thing either
From what I've seen of another 1400 outfit that I know about, it's almost unbreakable.
After riding the 1400 as a solo for a month or so, it's definitely smoother to ride, and the torque of the thing is really noticeable compared to the k. It's going to be interesting to see how that translates across with a sidecar attached to it.