FWIW, I solve this problem with ~/src/work and ~/src/personal. My default, system-wide config in .gitconfig are my personal creds. In ~/src/work, I have a direnv (http://direnv.net/) which configures my work credentials.

I used to do something similar to you, but this has been less effort to maintain/less repetition :) (which is nice, as our internal structure is lots of micro-repos so you're constantly cloning new things, and constantly adding creds becomes a hassle).