There's quite a bit of people talking past each other here. A transfer is a digitized file taken from a film. A release is a digitized file found on a DVD. A lot apparently happened between the transfer and the release in terms of added CGI, color "correction" (lol), soundtrack, etc. I have little doubt that the transfer done for the 2004 discs was probabaly excellent, judging by the detail. But that doesn't mean the release is good, or true to the originals.
It certainly makes sense to use the release with the best clarity to try and reproduce a decent facsimile of the OT. That is because colors are largely correctable, but sharpness is not. Content is also not correctable (obviously), except that people like Harmy and Adywan have managed to take great pains to try and restore those scenes that have been damaged.
We don't have access to the original transfers - nobody does except Lucas. And there doesn't exist a decent modern release. It should be obvious to danny_boy or any other SW fan that just because one would use the 2004 discs on which to base a transfer doesn't mean we think they are accurate, or that they are watchable. To wit, what do you think would turn out better, a 2004-based project that has been color-corrected and despecialized, or a 1993-based project that has been sharpened? The answer should be obvious (2004-based), but that doesn't mean that it has better colors, or is better watching out of the box. Because it clearly has terrible colors, especially ESB, and is full of inane distracting crap. Every indication is that the blu-ray will have even better detail, but it will still be unwatchable because of the crap done to it for release, and will therefore need to be fixed by somebody here in order to make it a reasonably watchable facsimile of the OT.
This is the only movie in the world in which this discussion is taking place. That isn't our fault, it's Lucas' fault.