The a200 is now a pretty low-end body. I'm not sure about what Minolta lens models used to test out better than comparable Canon or Nikon optics, but I doubt many of the currently produced optics are as good as Nikon or Canon's latest generation lenses. Both Nikon,and Canon have been updating their most critical lenses over the last few years--Nikon with its ultra wide zooms, wide zooms, macro lenses, and high speed prime lenses,as well as a few other lenses, like the DX ultra-wides and the DX wide zooms. Canon has been doing similar things, updating its lenses where it was weak in comparison with other makers' offerings, like updating the 24 and 45 T/S lenses to match Nikon's new TSE series, and also updating the Canon 100mm f/2.8 EF Macro after Nikon updated its 105mm 2.8 macro lens, creating a 200mm f/2 lens with stabilizer after Nikon created a 200mm f/2 lens with stabilizer, and so on.
Sony's new a850 looks like a nice full frame camera,at a VERY fair price! Sony now has a huge model lineup--what is it now? Eight d-slr bodies,isn't it? I dunno...are you happy with Sony? I know two somewhat serious enthusiasts who shoot older Minolta/ Sony a700 systems,with some nicer lenses like their 70-200/2.8 and 85/1.4, and the images they get look quite good. With Sony pushing the full frame price down lower than anybody else, I think it might be time to STAY with Sony,rather than leave them for Cannikon gear.
I'e looked at and held and demo'd some Sony stuff. The higher end has a nice "feel",and the ergonomics are,well, nicer than Canon in my opinion; Sony has a more mechanically old-school feel to me, which I prefer,and their ergonomics feel very "sorted" as the British say. Other people might prefer other brands of equipment, but I like the way the higher-end Sony gear feels and handles; their lower end stuff feels odd to me. YMMV.