I did the following to install (Although I could copy the whole ~/.vim directory to the new place instead of steps 3-6):
Install vim 7.4:
brew install vim
Note: If you are using mac operating system, make sure you create an alias in your bash_profile pointing to macvim i.e. which mvim
Add Plugin 'Valloric/YouCompleteMe' to ~/.vimrc and run :...
Over the past week I've decided I was wrong about re-running ClangUpdateQuickFix on a buffer containing the header not working. Although I would never have written that if I had not tried several times, it was probably all during the same session -- meaning I could have overlooked something such as having pre-compiled the headers with a different user.