I got a D7000 2 months ago to replace my D40 that I had for almost five years. The camera is outstanding, but the D5100 is very close, the meat and bones under the skin are pretty much the same. The D7k has more buttons, a different menu set, and a beefier body.
The 55-300mm I'm somewhat disappointed with. At 300mm, even with vibration reduction, I get some ghosting and softness. f11 is a good aperture for it outside. It is best at less than 150mm, which kinda defeats the purpose of the long end (on a DX digital camera I believe the 300mm is equivalent to a 450mm on film).
I don't own one yet, but an all purpose carry-around lens that I tried out and really liked is the 18-200mm f3.5/5.6. New, they are around 800, but I've seen several on craigslist for about 4-500.
The 50mm 1.8 is an amazing lens, it is especially good @ indoor photography without a flash.
Just like mods, all it takes is $$$$!!
my 0.02