Sell the D300s to finance a D7000 - in short no.
I acquired a D7000 a couple of weeks ago. I haven't really had the time to put it through it's paces yet, but one of the things I've noticed is that the ISO performance is not as good as it's hyped to be, especially if you shoot raw. Compared to my D90 I have about one more stop of usable ISO, which to be honest It's pretty much what I expected. The d300s and the D90 have a very similar, if not the same sensor, so I think the comparison will probably also stand for the D300s. If you you shoot JPEG, or use Capture NX to process the RAW files, then it's a whole different ball game. Nikon seems to have worked some serious voodoo with the noise reduction algorithms.
Would I buy a D7000 in preference to a D300s, well I did because the D7000 suited my needs more than the D300s did. Depending on another persons needs the d300s may be a more suitable camera.
That said, I was having a chat with one of the guys at my local photography shop at the weekend, and basically since the arrival of the d7000 they've gone from selling 30-40 d300s a week to selling perhaps one, and it also has appeared to have had an impact on the D700 sales as they're down as well. Now this may be partly down to customer perception of megapixels, but according to the guy serious pro Nikon users have also been buying up the D7000 for the resolution, and to use as a backup.