Sorry for the lateness of my answer.
I use Cam Scanner too actually, when on the road. I digitized the notes I took at a colloquium I attended Thursday-Friday with it. I think it does a good job overall. You can see my notes here: https://www.flickr.com/photos/tournevis/sets/72157649121587133/
But I agree with you that it is not a perfect solution. When I have the time, I scan my notes on my flatbed scanner, an Epson Artisan 800, and I send them to Pixelmator (on a Mac). In it, I use the “Select color” function to select the background cream of the paper, then use the “Fill” function to replace it with white. I can then use the “Reverse selection” and “Fill” functions to change the color of the writing and drawing, or even use more granular functions to change only some of the text or images. You can see examples of my cleaned out notes (and some not cleaned out) here: https://www.flickr.com/photos/tournevis/sets/72157643591558944/