Moving “up” in formats, getting a “pro” camera or the absolutely best lens to get better photos.
These all display the fundamental misconception that getting better gear would automatically create better photos.

Two years ago I moved up from a D40x to a D300.
What I saw was a more technically advanced camera and NO gain in the quality of the photos.
It took me a few months to grasp the fundamentals of the new possibilities…
I’m still learning new stuff at times and expect to be doing that for a while more.

The D300 compared to the D40x (D60 is the successor) has shorter response time due to more AF-detectors and other similar differences. The output quality though depends more on the fact of moving from CCD to CMOS (newer technology) than anything else. I believe we may have one step more taken as the D7000 came out… What the real difference is, really has to be pondered on, viewing photos taken under similar circumstances.

Why not begin with a ponder on where you show your photos?
Do you really NEED to have more than 8 to 10MP of image data, does the lens imperfections REALLY affect your photographs, would a “pro” camera body add anything at all more than technical complexity to your gear?

This actually got even more emphasized as the Nikon D800 came about; do you REALLY need 36MP? The camera creates 14 bit RAW files. As 14 bits need 2 bytes of recording space, the files end up containing 2 bytes per color component (4 of them in a RAW file) per “pixel” in the bayer array of the sensor: 2x4x36 million bytes = 288MiB, 275MB.
(Note: MiB = 1000^2, MB = 1024^2). Compression will reduce the size of the file that shows up on the memory card to 24-30MB I’d guess. 
Those 288MB is what the RAW-converter MUST compute to get you ONE view of the picture. Your computer needs to be THREE TIMES faster than one used for 12MB images (36/12 = 3 times more data!). Based on my guesstimated file size, the size of the storage volume required for the picture archive will double. Also the transfer speed to and from the archive needs to double. All these based on THE SAME amount of pictures taken and THE SAME time used for edits.
Do the benefits of the higher resolution overcome the bad sides of handling this amount of data?

My choice: Get a new D700 – which still is one of the greatest cameras available. leave the D800 to the people that really needs them.

A sidenote: The ENTIRE VIEW AREA of a standard PC display of 1280x1024px is equal to a 5:4 ratio 1.3MP print at 100DPI (a 17″ display). The same image can be printed onto a 5×4″ (125 x 100 mm) sheet at 260 PPI [1280/5 = 260, 1024/4 = 256] – assuming that the printer is capable of producing 260 PPI (many printers need a 6×6 array for ONE pixel).

This might good reading, considering the above!