Upgrading D200 to D300? Or better glass?

I've owned a D200 for the last two or so years right now, doing some amateur photography and simply using the camera for family event photos as well. For the most part I use the 18-55mm kit, 18-105mm DX 3.5-5.6, and AI-S 50mm 1.4 lenses.

Would my money be more worth into upgrading the body and getting a D300 for relatively cheap, or investing into more glass? If so, what lenses should I be looking at?