Anyone recommend the grip with the D600 and why?

Honestly maybe I don't shoot enough to understand but I have a friend that tells me that a grip is basically required hardware when I get this D600.  (He's a Sony guy)  I see some minor advantages to getting a grip but at the cost of $300+, that sures seems like a premium.

People say the D600 is a little smaller so the grip might be nice to "beef" it up a little.  I don't know if putting that money into a high quality prime lens might do better.  Grips always seemed like a luxury item to me.  Am I wrong?

Bryan