Will anything bad happen if I just delete my thumbnail cache?
This is a bit of a guess, but I'm assuming if you switch off the icon preview &amp; preview column, then the system would have no need to generate preview icons...

You might need to do this for all 3 view types, Column, Icon &amp; List, from View menu  > Show View Options  Cmd ⌘   J 
Example [using a RAMDisk, as it was just conveniently populated]...