Well, it is always inevitable, new technology comes out every year eclipsing the latest and greatest that just came out. Camera bodies are no exception. We have been riding the latest revision of the FX D3 body, the D3s, for some time now. While it had great improvements and a completely different sensor than the D3, it is still a little behind the game in terms of Megapixels. ISO sensitivity will be hard to beat in the new bodies, but I am sure they have figured out how to get another usable stop or more out of the new sensors.
With the latest news of a new body (D4 and D400) rumored to be announced in August of this year, I can only imagine how Nikon is going to improve photography once more. I can only imagine that the megapixel (MP) size of the sensor will increase. What I do not know if the ISO sensitivity will also increase. The issue with packing more MP's into the same size sensor is that ISO quality decreases. This is one of the main reasons why the D3x only goes to 6400. I think that is also why the D3s packs more of a punch than the 1D Mark IV from Canon as it is a higher MP sensor, ISO quality at high levels is left behind by Nikon.
Because the latest and greatest always seems to come out year after year, I say put your money into quality glass as it tends to hold its value a lot more than a body as the lenses are not revised year after year. I think quality glass is more important than what body you have. You can get excellent results from a D80 or a D200 with a great lens, than with a D3s and a crappy kit lens. Now, I am not a pro, nor do I make any money doing this, it is just from my experiences and results. Can't wait till August!