I have used the 18-135, I own the 70-300 VR, and I own the Tamron 90 AF-SP Macro. The 70-300VR and the Tammy are GOOD lenses, well worth migrating forward. What you will get, nowadays with any current Nikon APS-C body, is a MUCH higher-resolution d-slr, with MUCH cleaner High-ISO performance, wider dynamic range, and deeper, richer color.
Since the D80 was current, NIkon's cameras have moved to the absolute TOP of the APS-C sensor performance heap, and AF systems have become better, and more-capable. I would say the D7100 is the D80 replacement, only three full generations newer, and better. SInce the D80 was current, the "pliability", the "workability", the "quality" of the files has been boosted due to both in-camera image processing software and hardware, and new-generation sensors Nikon is using. All those things have together, increased image quiality, especially with the newer software, like Lightroom 5, for example.
I'm not knocking anything, but all I'm saying is that since the D80 was current, there has been a **major** increase in the "extended range capabilities" of the Nikon cameras. I'm not talking about impossible-to-see, minor improvements...I'm talking Pentium IV computers and Windows95 versus modern 4- and 8-core processors and Windows 8...
Things have changed, a LOT, at the high-end enthusiast's camera.....D80, D90,D7000,D7100...you're in for a SHOCK. By one measure, moving to a D7100 moves you "four generations" forward, by another measure it's "three generations". I cannot tell you if you do need a new camera body, or not. DOn;t know you, don;t know what you shoot, or how, or how much. Just saying, there's a new sheriff in town....