I have had a D90 for over 18 months which was my upgraded from the D40 and the difference was remarkable and well worth the cost of the upgrade.
I have just bought a D7000 a few weeks ago, with the rebate offer. I watched used ones go on eBay and the like for pretty much the same price (sometimes more) than the new ones are selling for (after deducting rebate value).
This is how I made my decision, so maybe it will be helpful to the OP if they are still considering it:
I love my D90. I had no desire to upgrade it for another good year. But the rebate offers and the price drop since the release of its successor the D7100 closed the gap between the cost of selling my D90 and buying the D7000 so it seemed an optimal time to buy.
Now for what my decision was based on, aside from the cash outlay:
I am very practical so I won't pay for bells and whistles unless I specifically need them. For me it was the sensor and improved ISO/lowlight performance. Since having the D90 I have been drawn to low light and night photography. For me the small difference in the cost of upgrade now was well worth it because what I am paying for is going to enhance an area of interest of mine very specifically. The extra focus points, movie capabilities ..... nice, but not what I based my decision on, because they weren't enough to sway me as stand alone benefits for the upgrade.
Have a look at the cost to upgrade, check a side by side comparison and figure what features would help you in your photography, in line with where your photographic interests/style lie, and then work out whether those extras are worth whatever it is that you are spending to upgrade. I figured under $200 gave me a lot more camera and spread that over the at least 2-3 years I will be keeping the D7000, I know I made the right decision