Having digested it a bit more, I like the A550 more and more. To me the key weaknesses of the A350 include lack of precision live view, low res screen and low fps rate. All those are addressed in the A550, and as far as I can tell I wont lose anything from the A350. The bigger viewfinder is a minor plus. I'd prefer if they stuck with CF but going SD isn't going to kill me. Oh, the switch to Exmor sensor should hopefully mean an A700-like level of high ISO noise performance.
Personally don't care about face detection, but the built in HDR mode sounds interesting. Given how typical PP HDR works, I wonder what the output will look like. Particularly how good is it at alignment?
Discussion elsewhere claims the processing engine is a new one, so that might mean in camera jpeg quality particularly at high ISO will finally catch up with those of other brands. Also there is apparently no mirror lockup option nor DoF preview.
Somehow I don't think my A350 will trade in for much... might as well find out what the shutter limit of it is