I got a set of climbing specific wheels and wanted a cassette that would leverage that even further. The 32-11 was a good call. I really don't use the 32 that often (most climbs are fine with the 30) but when you hit a wall and need just a little more leverage and a little more confidence, the 32 is nice to have. I was worried about chain length because my other wheelset has a 30-11, but I have had no problem. If I was moving from a 28 to a 32, I'd probably need an extra link or two, but the 30-32 switch has performed fine on an Ultergra Di2 longcage derailleur.
I recently had to replace my rotors. The original equipment was Ultegra, but I always thought that the black interiors of the DA's were jsut cooler looking. According to the literature, they are slightly lighting and the black brake fins disperse heat better. That may be the case, but I can't say that I really saw a performance difference. But the DA upgrade was only a few bucks more, and they do really improve the look in my opinion. Usually, I would opt for performance over looks or cost, but in this case I'll probably always stick with the DA's.