What is the difference between the free and paid version?
Viewing post in Amelia's Stranded Adventure comments
The images are run through an upscale which should result in a crisper image. Pretty much all images in-game are 512x512 dimensions, and the upscale brings that to 2048x2048 (Android is 1024x1024 due to limitations). The images will stretch to fit whatever screen they're on, and the 512x512 results in a more blurry image because of this. This is also why the HD version is much larger.
It's a visual upgrade to those who might like to support the game.