So, I got my Sennheiser PC360.
I'd say they're a bit of a mixed bag. On one hand, the physical design is a nice step up from the PC350, but on the other, the sound is not necessarily an improvement. The spacial imaging is definitely better, but the tonal balance is off, at least to me. Maybe it's just because I'm used to the rather bass-light PC350 by now, but these sounds noticeably boomy in comparison. The midrange is also recessed, as a result.
Still, I fixed them up with a bit of an equalizer, and now the tonal balance is perfect. They sound exactly like the PC350, except with better spacial imaging. I used to always say no to equalizers...but they can be handy in a pinch.