If you are a casual user then switching to the A55 doesn't make much sense, especially since you won't need such high end features. With the A mount the lens selection is the same and here also you won't save much weight.
Better if you look at the m43 options like Panasonic and Olympus or APSC options like the Sony NEX or Samsung NX series. My NX10+30mm/F2 pancake only weighs around 400g.
I personally think the translucent mirror on the SLT cameras is neither here not there. The future is losing the mirror/prism box. EVFs will become better than OVFs, and contrast detect will become preferred to phase detect AF.