There is no need to delete ~/Library/Application Support/audacity/ when installing a new version of Audacity. Versions of Audacity before 2.1.0 do not support Yosemite.
You can use the same unofficial procedure as in 2.0.6 to display a custom theme - the process still works https://forum.audacityteam.org/t/old-experimental-theme-support/36966/1
If you have a Portable Settings folder in the folder that contains the 2.1.0 installation, delete Portable Settings then 2.1.0 can use the contents of ~/Library/Application Support/audacity/ .
Gale