If you are primarily unhappy with the blurriness of your photos, and you are shooting with no flash, then you need to fix two things:

1) unwanted movement of the camera, and 2) shutter speeds to stop the action of the subject being photographed

For #1, as you've suggested, a monopod will help steady the camera. Another thing that will help is to use a lens with vibration reduction.

For #2 (to stop the action), increase your shutter speed to a minimum of roughly 1/250th or 1/320th of a second (faster if possible). I'm making an assumption that the stage is fairly well-lit, but still dark. In order to accomplish these faster shutter speeds, here is my suggestion:

a) set your camera on manual exposure and auto focus

b) set your shutter speed to 1/250th

c) open the aperture as wide as it will go for your lens (f/3.5 is wider than f/4.0, for example) so it will allow more light to hit the sensor

d) use center-weighted light metering so your meter can give you a reading from your better-lit (center of the frame) subjects and minimize the effects of the dark background

e) adjust ISO upwards until your meter says you're within 1 stop or less underexposed. I think 1600 is probably the practical upper limit for ISO with the D7000, based on other references online. The reason I say "within 1 stop" is that you want to use the minimum ISO that will allow you to get the shot, in order to keep the digital noise minimized. Also, since you're shooting RAW, you can push exposure somewhat lighter in a post-processing program.

The costly answer here is that buying a zoom lens with vibration reduction and a large maximum aperture (f/2.8) will allow you to push up shutter speed a little further without having to push ISO up as far. You can get a less expensive lens with a large maximum aperture, such as a 50 mm f/1.8, but the lack of zoom limits your ability to take pictures as a spectator at an event.