For those of you who have the '93 Laserdiscs, I see positively no reason to purchase the DVD. You already have an official version struck from the exact same master. Having an LD -> DVD project is nothing more than an archive of material you own so my statement above applies in your case as well. If you aren't selling rips, and you shelled out friggin $250 for the Definitive Collection set, you've made a nice payment towards that Star Wars license.
It would be an interesting legal argument that you'd probably lose if you had a pirate of the official O-OT DVD as your archive, but even that would make an interesting case that has yet to be tried. I think you'd actually be in clearer territory just owning the X0 project or whatever as the definitive archive of your LDs.
Disclaimer: I'm no lawyer, so none of my statements are legal advice. Just legal speculation.