Well, I am of the school where I think you could fix up your road with a boxblade and scarifiers.
Sure, the other methods will work too, but as you said, if you're gonna get an implement you might as well get one you can use for many other purposes. If it was me, I'd lat least want to give it a try and do it myself. If it doesn't work out you still have it for everything else you will be doing with it. Just be sure it is a heavy duty model with weight and beefy construction as THE major requirements. You can always add weight to it.
I have done my 1/2 mile dirt road and almost have all the rocks removed with my boxblade. It is now almost 100% decomposed granite. A couple of the guys who posted on your thread, (Eddie and Brian) have visited my property and can tell you what they thought of the road. Of course, I like to do things myself and use what I got, I am hard headed that way.
Now that my road is smooth and in good shape, I would consider one of those road graders like Brain has to maintain it. But to get it there, I used the boxblade.
I don't know how a road boss grader blade would do on a gravel road?