I went from a R1150R to the R1200R and have to say the difference in engine and braking performance and overall handling is quite substantial. The R1200R is much more nimble, pulls harder, stops faster, runs smoother, and just feels more refined in every aspect to me. The upgraded ABS with linked brakes is excellent, the headlight is better for night riding, better fuel milage, etc, etc.
The R1200R is 75 pounds lighter with 30 more HP.... that was a big step up and the main reason I think the 1150 felt old, underpowered and very heavy when compared to the R1200R. Flickable is not a word I could use in good faith when describing my 1150R, while that's exactly how I could describe the R1200R.
Having ridden over 80,000 miles with almost no issues on my R1200R it's also easy for me to say that BMW's made a very reliable machine and mine is the first model year to boot.
While the difference between the Hexhead 07'-11' like mine and the new Camhead 2012's isn't quite as huge like the bump from the 1150 to the 1200, I'd imagine there's further refinements that I'm not aware of having never ridden one and the Classic's can only be improved compared to how I describe mine. ( Not enough for me to trade mine in quite yet though)
Like dbrick mentioned it's up to you to figure out how one bike makes you feel over another, one thing for sure, not one time have I had any regrets for trading up to the R1200R. It's everything I wished the R1150R was but could never be.