My Sony blueray player upscales my DVD's to 1080I, and they do look much better. But then I'm watching them on a Sony CRT widescreen, via DVI/HDMI, that has a native resolution of 1080I. Not as good as blueray,which my set displays at 1080I, but certainly better then 480P, which my tv also does natively and even much better than 480I which my set also does.
Upconvert isn't HD, so stop calling it that! I have a DVD player that upconverts, does it make it look better, Um No it makes it look like your watching tv through a screen door! And 4x3 Black and white upconverted by no means looks better then SD channel version.
D* SD is pretty good on my set since I feed it a 480P signal. Again, the CRT native 480P signal is what probably makes it much better viewing than on plasmas or LCD's. I was at a New Orleans hotel a few weeks ago, and I'm pretty sure they use D*, and the SD picture was horrible on their HD tv. But here at home, as I said, the SD pq is pretty good on my set.
So if you don't see an improvement on your upconverted DVD's, it could be those newer TV's. Just a guess.