Yeah, I hadn't even thought to mention that. Plastic bodied DX lenses may be weaker but they also weigh a lot less than metal bodied FF lenses. I don't plan on shooting in a war zone anytime soon so I think I can live without the pro-grade metal finish.
Nothing wrong with going with inexpensive gear. Had high ISO issues not been a problem I would stay with a crop camera. You get the sharpest results by using the best part of any lens out there. You also get that extra reach. I may pick up a D300 or a D7000 (D90 replacement) as a back up camera. Crop cameras are very useful.
Many bird watchers and sports photographers would rather use a crop camera than slap a 1.4x extender between a lens and a full frame body.