Writing music in StaffPad is great but that is if you concentrate on getting the note shapes you want drawn correctly . Apart from that being a pain sometimes it can detract from your creativity when you keep getting the sketch wrong.
Putting on my software hat I think what would help a hell of a lot is a small floating pallet.
Normally the pallet is invisible until say, one presses a stylus button. The pallet would move to where the stylus is currently at . On the pallet would be icons of all the usual note values together with anything else that is used frequently,...rests, ties etc.
When an item is picked up form the pallet it's icon (say a minim icon) , the pallet disappears, but the selected icon's shape follows the stylus pen tip while one chooses the spot they want that item to go. Tapping on the score places the icon at that spot.
That would take away all the pain of having to be careful drawing the shapes at the same time not detracting from the overall ideology behind StaffPad.
The user can if they wish still draw the shapes in the normal way.