I don't understand why you need/want another DSLR. In the film days you could never have too many camera bodies to load with different film speeds, slide/print film, color/B&W and so on. In the digital world that kind of stuff belongs to the world of post processing, so you grab the body with the best sensor you need/can afford, shoot RAW or high quality jpg, and leave the rest to Photoshop.
What lenses do you have for the Nikon? My hunch is that you get more value for your photography from another lens than from another body.
Just my 2c.
Frank