I think the last two or three seasons of Voyager still have fairly good CG. BSG is still probably the high water mark for these things, in part due to the disappearance of space opera from television in the last few years, heh. But Voyager looks good later on. Same with DS9. (Enterprise looks pretty fantastic, still. Its pilot isn't even eleven years old, though, but when we consider how far the gaming industry has come with regard to CG in that time, this is truly a testament to Trek's triple-A special effects crew.)
It is starting to show its age to some extent, though, I agree. Later DS9 and most of Voyager is really going to be a tough job if the HD releases do make it that far: low-resolution CGI shots will need to be completely replaced, and there's more emphasis on lots of cool space explosions and whatnot, so there's more work to be done.