I know this post is a bit dated..... I just found it. I've had good luck restoring gravel in my old homestead up north with a rototiller. I actually rototilled a friends driveway (probably 50 feet long) and it "fluffed" up the gravel and helped me rake out the potholes. The rototiller I had was a heavy duty rear tiller with a 11 hp engine - BCS was the brand. I set it to just go about an inch or two deep and idled it along which slowed the tines down quite a bit.
I also used a 4' x 4' drag harrow behind a garden tractor to drag a 300 ft driveway to "fluff" it up. Routinely use roundup to keep weeds from getting established.
Cleaning gravel - it's easy to make a screen, I've used two 8 ft 2x4s for the sides about 2 feet apart screwed together to make a rectangular box. Elevate one end about 4 feet. Attach "screen" to the bottom and shovel the gravel into that - as it slides down the junk will go through the screen-adjust the tilt to balance the speed with the mixed in junk so it falls through. The screen has to be strong, I used metal lath which has about 1/2 x 1/4 inch diamond shaped holes. Metal supply places sell flattened "steel expanded metal" in 10 or 11 gauge with different hole sizes.
Another method is to use a traditional cement mixer. Shovel the gravel in with lots of water and keep the hose running as it mixes, dump the water out and repeat.
Remember, that gravel is "there" somewhere, you don't have to keep adding it once you've created a good base.