I have never thought of Nixon as a good OF. Like you said he puts a lot of effort out... but it seems like he tries to do too much when it would be better to just cut your losses and make the play you can make.
A good OF doesn't always have to be blessed with unbelievable skills... just a good head on his shoulders to know how to make do with the tools he has.
I wish there was a little more Nixon in Sheffield sometimes... but at least when he coasts to balls in the gap to play them off the wall, he isn't diving to make the play and giving up extra bases. The key is to find a successful medium.