Re large cache...
Wavepad Version : Latest.
Ended up having the same issue, wavepad using up hundreds of gigs. After much research on wavepad tool, finally found a solution that worked for me. I wasn't able to access the Wavepad folder from Library/Application Support through folders navigation either.
Solution that worked-
Open Wavepad>Settings >Audio> an option exists by field name, "Cache File Retention" towards the bottom of the pop-up and options like within 28 days/14 days/upon exit. There is button to delete the cache files "Delete unused cache files now". Without having to clean up manually, I used this option to clean the Library/Application Support/Wavepad folder of unused files.
Hopefully it works for a few.
Thank you-