I found that DVDs do look better fed through a superior upscaler like the one in my Oppo. The one built into my OLED or AVR isn't as good, even for Blu-ray. The Oppo wins all round.
I think a lot of scaler chips fail when it comes to chroma upsampling. 4:2:0 chroma compression is very resolution lossy when it comes to certain heavily saturated colours, particularly strong reds, and how well those colours are scaled back to full res are especially important for something like DVD were the resolution is low as it is.
Blocky, bleeding reds make me weep inside.