It's easy to stop the OSD themes being 'animated' just by editing the osd.xml file.
Make <fadeaway> 0 and <fademovement> 0,0 throughout the osd.xml file (there are likely to be more than one instance).
In 0.21 it'll be possible to do that just by editing a playback profile.
As for the horrbile yellow/orange folder images - you can certainly change them but I wouldn't recommend removing them since they're needed to highlight the gallery item selected.
Copy your own files into the root directory of a theme called mv_gallery_back_reg.png and mv_gallery_back_sel.png - The _sel image is the one used to highlight a selected item.
Likewise there are mv_gallery_folder_reg.png and mv_gallery_folder_sel.png files which are used for representing directories.
Oh and lastly there's mv_gallery_dir_up.png which is the 'up one dir level' icon.
It kinda sucks that the theme is supposed to define all images & fonts but some are still hard-coded.