Replaced /usr/bin/vim - now I get error messages
This is a known issue. From :help MacVim:

Note: Starting MacVim by creating a symlink to &gt;
    .../MacVim.app/Contents/MacOS/Vim with 'ln -s' does not work.


I found a lot of people getting a string of E254 errors from using a symlink. See this ticket on the MacVim issue repository. The solution follows:

    Most likely this is because you have symlinked directly to
    the Vim binary, which Cocoa does not allow.  Please use an
    alias or the mvim shell script instead.

MacVim comes with a startup shell script, mvim. You can alias it to vim if you'd prefer to use it instead of the system vim. If you want to start vim in the terminal rather than as a gui application, set the alias to mvim -v. Add export EDITOR=vim to your ~/.bash_profile to make sure that any terminal applications are using the now-aliased vim. This should cover all your bases.