Have you looked at the D300 forum? There has been a lot of wailing and gnashing of teeth over there about the lack of a "D400", whether the D7100 is an adequate successor to the D300, and what features are missing in the D7100 that invalidate it as a D300 successor.
I came to the D7100 recently from the D90, which was a smooth transition and (in my humble opinion) a significant step forward that gives me (and maybe only me) all that I would have asked for in the mythical D400. However, some (but not all) dedicated D300/D300s shooters who do not feel the same way about the D7100 as a way forward for them.
I think it all boils down to features. What do you want in a crop factor body that you do not have in your D300? What aspects of the D300 MUST you find replicated in a crop factor body with a next-generation sensor? Only you can decide whether the advances in the D7100 are sufficient to overcome the D300 crowd's reservations -- most of which, in my rather naive view, seem to revolve around the fact that there are "pro" features in the build and layout of the D300 body that are not found on the D7100.
I think the D7100 is a pretty amazing camera, but I did not come to it from a D300/D300s perspective so I may not recognize what all the angst of D300 shooters is about.
After that long-winded preamble, here's my advice: get your hands on a D7100 and see whether, for your intended pattern of use, the deficiencies perceived by D300 users are important to you. If they are, hold out until fall to see if Nikon actually turns the myth of the D400 into reality.