I moved from the Sony a550 to the a77. I have some really nice pictures with the a550. I have looked back at my a550 files and in my opinion in terms of IQ there is not a whole lot of difference between the two when it comes to vacation and family shots where there is not much cropping needed or a specific target to capture from a distance. However, for me there is a big difference in the two if you are shooting small targets with long lenses and in some other situations. The a77 AF is much better plus focus peaking with manual focus has made certain types of shots possible for me that were difficult for me to get with the a550. Specifically shooting humming birds. I really had trouble getting usable shots with the a550, especially using AF, while most of my shots with the a77 are usable in terms of being in focus. Furthermore, since my vision is not good enough to focus manually without the aid of focus peaking manual focus was not a good alternative for me when I had the a550. Additionally, the a77 realty made a huge difference with my Tamron 200-500mm lens in terms of AF usability. I had bought it to shoot water fowl. With the a550 I had poor AF performance with that lens. After spending a week with the two on the coast shooting birds I was on the verge of selling the Tamron. Subsequently after using it on the a77 the results were so much better I decided to keep it even though I also have a Sony 70-400mm G.
One other difference tween the two that would only indirectly affect IQ. The placement of the a550 view finder was such that, as a glasses wearer, I really had problems seeing the whole scene through the finder . That is not a problem with the a77. In fact I could use the EVF without glasses if I wanted to.
Bottom line is that, while I also would like a copy of the Minolta 70-200mm G, in retrospect I would nothave chosen it over upgrading to the a77.