Will I notice a difference in pic quality with progressive scan or upconversion?

I have a Sony Wega CRT HD Display that accepts 480p and 480i as well as 1080i through component input. Should I buy DVD player that upconverts or should I buy a dvd player that is progressive scan. I just want to know if I should invest in an upconvert dvd player or if a progressive scan dvd player will do. Thanks for the help!