would setting visibility to invisible for objects outside layout speed up the game?
Nope, this will have no effect.
TW, typo in the Performance tips
ould fullscreen mode set to crop and manually scaling all your sprites on their creation be faster than fullscreen set to scale?
Probably not - if it's hardware accelerated it will probably have no effect either way, but even if software rendered, scaling sprites is probably as much processing as scaling the whole display.
set global variable to read return function
Generally it's not possible to answer "Is X efficient?" questions, especially when involving third party plugins which isn't our code, but I would guess if you're only doing it 10 times a second it will be perfectly fine. (FYI I've built-in the AppMobi accelerator to the Touch object for the next build)
ill setting the animation speed to 0 for one frame only objects make a difference?
Everything important has been mentioned in the Performance Tips manual entry - anything not mentioned there is probably not likely to have any significant effect. Any important little tweaks you can make to improve performance are already written in the article.