DSLR or lens upgrade?

I have a Nikon D3100, 50mm 1.8g, and 55-300mm 4.5-5.6. I want to upgrade my DSLR to a D7000 and get a Tamron 28-75mm 2.8. I just don't know which to get first. What do you think would be the smartest buy?

In most cases it is better to add to your lenses, however when you upgrade from the entry level D3100 to a semi-pro D7000, you will add to the number of lenses you can use to fill your system, including legacy manual focus AI lenses.

You can always add lenses later including any of the older Nikkor AF lenses.