I have had many RC51s but for awhile I had only a 2009 CBR1k (it burned oil? which was really cool....not) I did all the mods in the book to that bike, but in the end it felt "hollow". I never managed to use inline-4 power on the street and it was just another cookie cutter bike. What really bothered me was when I would go to a bikenight and there would be 15 just like it.
I ended up selling the CBR1k to get my current 2003 SP2, I will never sell it or be without a RC51 ever again.
The character of the bike, ownership experience, forum strength, cult-like following, amount of online data, and the people I have met through ownership are just a a few of the reasons I keep the RC around.
The RC51 makes the perfect amount of power and has the perfect powerband for my type of riding (backroads, mountain twisties, 60-120mph). It responds to modifications well and when those who know what they are looking at see it; it still drops jaws.
Both are torture racks for passengers, The RC is comfy for me and can be made relatively comfortable with a seat, clipons, and tank grips. I prefer the V-Twin, gear-driven configuration to 4-bangers, they really are not that much better unless your regularly doing 120+mph regularly.
....can you tell? I like RC51s