I've done the switch from a 128i to a R56 Cooper S and this is one of the worst decision I've ever made.
I've always been a MINI enthusiast and I currently drive one but those cars are rattle cages. I've had mine for 6 months and it feels like I had it for 6 years...
Now I'm on the hunt for a 2013 135i and while the 2 will probably be a good car, the 135i will become a true icon and a must have car in a couple of years. Like the 2002tii before it the 135i will become a legend in my opinion.
I'd never think twice if I were you and go for the 135i or keep the one you currently have.