I thought i was not doing things right too - and have spent alot of time optimising, and trying to fix things for mobile, which work fine on desktop. have read alot of other peoples problems and resolutions here and elasewhere for pointers too!
On the starling side, I'm still getting returned somewhat randomly to the android desktop from time to time, with no indication of what could causeing that to occur.
the only other big starling issue i had was rendertexture larger than 1024x1024 either being invisible, or causing a return to the android desktop whenever used ! (worked around now)
Using profiling, my performance issue appears to be Box2d Alchemy alone ! mainly it's Presolve and Postsolve taking a crazy amount of time to process (<3ms on desktop, >50ms on my android device !) - everything starling works great and framerate stays at what i set it to be - - - until a box2d collision occurs ! (something i should take to a different forum )