The games wouldn't look any different considering you have the exact same limited hardware resources.
The dreamcast couldn't get over it's hardware limitations, but this still doesn't mean games wouldn't look any better than before. The dreamcast died pretty young and didn't get to experience many games that pushed it. Shenmue 2 was completed near the end of it's life cylcle with old tools( from the psx era) and it looks pretty amazing. I can understand how the games graphically wouldn't look that much different, but I still think art and aesthetic design can surpass hardware. In my first post I should have rephrased my question to mention more about aesthetic design; I meant say how much better dreamcast games would look if they incorporated modern aesthetic design.