In March 2008 I bought a '08 RT and had it for 2 years, in which I drove less than 5000 miles. In March 2009 I've got my C14, so during one year I had both on the stable.
During that time I did 10000 miles to the C14 and 400 to the RT. They are just different things. My girlfriend likes the rear seat of the C14 better, and considered the RT to be a car with 2 wheels. Pretty good comparison, actually.
The RT allows you to go at your pace and see more of the landscape, with a more relaxed, touring position. The Kawasaki puts you in more of "attack-mode" and explore the boundaries of your comfort-zone, with the knees in a tighter angle and a harder suspension. Me? I love the Kawa, but it's just me. I never "clicked" with that boxer engine: noise, vibrations, torque... everything seemed wrong. Again, to me. If you like it, then that's the bike you should get.
Maintenance wise, I can't say anything bad about the BMW, but I had it very shortly. The Kawa can be expensive if you do all the non-sense in the manual, like checking your valves every 15000 miles or whatever it says, or changing those Iridium spark plugs every 7500 miles. Even my dealer (Kawasaki official dealer) refuses to change the spark plugs sooner than 15000 miles. Oil changes and such can be done by you if you fancy it. I don't. I let the bike at the dealer instead and get loan bikes to try, and enjoy driving instead of wrenching, specially because my garage is useless, unheated and poorly lit, and another 170 cars park there in the building.
To wrap up, the upside of (or the reason for) a higher maintenance is that you get a much higher performance bike, and that needs more attention. Just like a Tomcat needs more looking after than a Cessna 172.
