D70s is a great camera, but if you are asking about upgrading, then you probably have some idea thats what you want to do.
There are quite a few used D80 ( £320 ish ) and D200 ( £420 ish) models, the Fuji S5Pro is available for around £420 refurbished from Fuji but its aimed at portraits weddings and studio work mainly with its wide dynamic range. You could use your lenses comfortably with those, but i doubt in most cases that you would see much difference in the resulting images ( apart from the Fuji).
The D200, I found, is nice to use, it has a few more features than the D70s that you might find useful, and a bigger lcd screen.
D300 is a more expensive upgrade, bigger screen, good high iso capability and more modern autofucus among many other things. But if you are thinking of full frame, then thats a whole new ball game. You would probably need new lenses or make sure the ones you have are FX compatible, then the only route left is better lenses.
There are lots about, you dont have to spend mega bucks and there are a few " consumer " grade lenses that wont break the bank but give results close to the expensive ( heavy) lenses. If your looking at 200mm, I can recommend the Nikon 18-200 VR as a good lightweight walkabout lens. Sigma do a nice 70-200 f2.8 and Nikon do an excellent 80-200 f2.8, both around the £590 mark.
You could get one of those and keep the D70s then think about upgrading the body later.
There is always a ready market for a used D70s ( me, for instance
) but you wont sell it for too much and prices are dropping as the newer cameras come down in price.
Hope thats given you something to think about
Allan
