Unless you do something weird with your settings, transients will just make your code harder to read without adding any measurable performance value.
People that want performance should use object caching and page caching and your current code is probably already the best there is to utilize them. Transients will add almost nothing for them.
Transients make sense when you want to save several DB queries or network access, but your theme mods are already retrieved in one query from the DB, no way to improve on that.