I'd get the lens. At less than $900, you're not going to take much of a hit if you resell it later to move to FX. And, while the idea of 2 bodies sounds interesting, it makes most sense when the two bodies are the same. These cameras are complex (as you probably know) and learning them takes time. Switching between two different cameras can get confusing. When I got my D7K, I kept my D100 for a while, thinking it could help cut down on lens swaps. But the two cameras were so different that the only real use for the D100 would be as a backup if the 7000 bit the dust. So I sold the D100. I have the 17-55 and love it. I bought it after trying a 24-70 for a couple of weeks and decided that I needed more room on the wide end.
I also have no need to consider FX (I might want FX, like I want a Ferrari), but as a hobbyist there's no way I can justify the money and the sacrifice of added distance on my long lenses
Jim Singler D7K with a bunch of lenses and other assorted stuff