^Probably the best thing I did for myself was taking zoom out of my hands.
It's always worth it to have better glass. If you're thinking Nikon for the next camera body then investing in better glass that's going to work with the next body is where I'd put my money.
I personally have the 50mm F/1.4. It runs about $220 last time I looked and it's built like a tank and I probably take half my shots with it.
If you're wondering if 50mm might be too limited, here's a photo thread entirely with the F/1.4.
St. John's, NL - 00:39:52@50mm [50 images]