Your worries are pretty much groundless - there are a lots of "original" (Nikon/Canon etc.) lenses who are POORLY built (lots of wobbling, lots of plastic in them and so on). On the other hand, there are many "third party" lenses (Vivitar, Sigma, Tamron, Tokina...) which are EXTREMELY robust. Two of the Nikon's poorly built lenses: kit 18-55mm, plasticky, narrow and flimsy (manual) focus ring etc.; 18-135mm, same thing; three examples of a high quality built third party lenses: Tamron 70-300mm VC (compared to Nikon 70-300mm VR, it exhibits less wobbling, feels "tighter"), Tokina 105mm f/2.8 macro, Sigma 17-50mm f/2.8 EX DC HSM OS... Situation was slightly different back then, during the "analog era", when Nikon lenses were a synonym for robustness and "heavy build", though even then, a company by the name of Vivitar (which, allegedly, used Tokina's facilities) made a lot of extremely robust (and optically perfect too) lenses with Nikon's F bayonet (as well as for many other camera producers)...