Previews of video files, images, album art should be bigger. Things just look better when the previews are large enough that you can see details. I set Nautilus previews to 100 pixels, while leaving folder icons the default size. It would be nice if Nemo had the ability to change preview sizes built in.
I mean look at how much better the 1st preview image looks then the current setup. You shouldn't have to squint to figure what file you want to open.