I'm ripping a client provided dvd using imedia converter to prores422, editing in fcpx and even though the original is SD shot ten years ago, it's still slightly sharper and has more detail than the rip.
Yup...sorry to say. You are taking a compressed format, and recompressing it. And then you'll recompress it again to the DVD format. It will never look as good as it originally did. This is why having access to the originals...the original media and project..is more desirable than making changes to a project with only the DVD as your source.
I disagree with Shane.
If you rip to a 422 codec (eg Prores) it should look as good as the original.
If you recompress to DVD and have a good encoder, it should be very hard to tell the original from the new one.