This was a very popular request. If you want to replace your abilities with smartcasting, go to your Keybindings. Smartcasting is virtually always an improvement once you're comfortable lining up skillshots w/ the champion you're playing. I play w/ it exclusively, and much better players than myself do as well.
I mentioned Ezreal, but other really heavy combo champs like Veigar and Leblanc it is virtually necessary to smartcast if you're going to pull off your full combo on a consistent basis.