I use this feature a lot in PS Express, and only bought PS Touch because I wanted to save files without loss of quality, so I'm dismayed that it's not available!
And why can't pictures be selected from the gallery in most recent order first, as you can with PS Express? It's a pain to have to scroll through from oldest to newest to reach the pic I want!
I would imagine Clarity is close to Sharpen. (FX icon (3rd icon from top right) > Basic > Sharpen.) There are other tools too based upon what you're going for.