Sorry to burst your bubbles guys. But any changes to the size or the resolution of the screen is technically unsound.

Increase of screen size will make the graphics look even more pixelated. And any change of the touch screen size will affect the gameplay of games (bigger marker in EBA an Ouenan anyone?).

And changing either of the screen only is out of question. What will happen to some games that uses both screen for gameplay (example: Sonic Rush and Yoshi's Island DS) if that situation happens...

Touch Screen > Analog nub

If you talking about FPS....