I don't have one myself yet however from recent reviews of the New 3DS's the screen is not only bigger but also more sharp, brighter, more vivid and has better viewing angles when compared to the old 3DS's screen.
Which translates to both 3DS and DS games looking more sharper and more vivid on the New 3DS's screen despite being bigger, than the old 3DS's screen (meaning less pixels per density).
However this should not be a solo deciding factor for upgrading to a New 3DS from an old 3DS, you should have and there are many more other reasons why the New 3DS is worth waiting for and worthwhile upgrade.