Upload & Sell: On
I would love to get the D2x but after further thought and the comments here, perhaps I ought to be thinking of picking up something like a used D300 instead. It seems to me that in good light the D2x will perform well, and I would hope to be able to bring out the best of the files in Lightroom, but as previously mentioned, I would also be using the camera in doors capturing family moments almost on a daily basis. Seems like the D2x may struggle here without flash, and the D300, with its better ISO performance and on board flash might work out a bit better on that front. I hear that the D300 AF is very capable, so would be adept at catching the action as it happens.
The D300 AF is not very capable... it's amazing. It's essentially the same AF module as in the D700 and D3, with about 95% to 98% of the performance (the D3 is a hair quicker, probably due to higher voltage) and even better coverage because the AF points cover a larger part of the DX frame. I put over 100,000 clicks onto a pair of D300 bodies shooting aviation (see this old thread for some examples), and the D300 absolutely rocks.
There are better high-ISO bodies than the D300 (D7000, D5100, D5200), but since you want fast AF and a rugged build then the D300 is probably the camera for you.
As regards landscape work, both would seem be rugged enough to cope and take a beating. IQ and DR on the D300 perhaps a little better?
In the end, 12 MP will be a great improvement over the D50 (now dead), and I’ll have the ability to print bigger. Having greater low light capability is a plus for indoor and family pics. 2013 may see the introduction of the mythical D400, but who knows. In the interim, whilst saving for better glass (currently using Nikon 18-70mm) and keeping my ‘big purchase upgrade’ options open, I need something that will meet my needs over the coming months but also be a joy to use.
Joy to use, check.
Larger prints than what you can get from the D50 and D2x bodies, also check. Rugged enough, definitely.
What I would also definitely suggest is that you pursue more glass. For your indoor family shots, something like the $100 "nifty 50" (50/1.8D or G) would give you at least a 2-stop brightness advantage over your 18-70, and sometimes more. There are all kinds of old, manual-focus prime lenses you can mount on a D300 which will give you great results for very little money (for example, I have a 28/2 and a 35/2 that each cost me around $200 or $300). And on the much-more-expensive side, my personal favorite lens for both landscapes and portraits is the 70-200… And that new 70-200/4 looks absolutely scrumptious.