Have you tried setting the file display toolbar's image to large? If the 32px icons are too small as well then have a look at this iconset Directory Opus 10 Default XL Toolbar Icons - 250 icons!
Its the same as the standard icons but then in 48px. You can put that icon set on top if you wan't all your buttons to be 48x48.
As for the folder tree buttons. I found out that if you use a large File diplay toolbar and turn on Settings>File display>Border> Align other lister element headers with the file display border. then the folder tree header buttons wil get a larger click area, it won't enlarge the icons but the buttons wil get bigger according to your largest icon of your file display toolbar icon.