hey,

until you dont want remake every grafic you should stick for a resolution of 320x480 and then scale up for higher resolutions. its also useful to design GUI elements with some space to every border so if a device miss some space it still fits the screen

in my Math Warrior the backgrounds grafics are slightly bigger then the screen so it fit the most resolutions

since i got some problems too with the different devices and was asked alot how to fix, i contacted a friend of mine who use HTML5 to develope for android devices, he was telling me that he always gather the resolutions of the newest android devices and some mid-range products that have similiar resolutions and he only design to fit this devices, the rest is just bonus he said

the ouya might be a special case where i personally would make a version just for the ouya to deliver a good quality product and be a part of the minor goldrush it might bring

if i totally missed the point i still hope it is somehow useful