The ability change the size of thumbnails would be nice especially when viewing on a mobile device.
Have you tried:
Settings --> General --> Allow for more covers and photos?
Just two options, but quite useful.
Allow for more covers… Is not yet available for mobile.
Mobile as in phone, I was thinking tablet.
On the thumbnail size issue, if I exclude (Audiobooks) via tags, the top edge of the top row of thumbnails is obscured just enough to be annoying.