However, it sounds like the dealer is correct in telling you what needs to be done. How they went about doing the other stuff is another story.
The shakes from the brakes a probably due to a warped rotor or two. You don't have to go off-road to warp your rotors. It is simply a matter of your brakes heating the rotors up and then the rotors cooling down. If you drive aggresively or have to brake hard sometimes, that could be a small part of the cause. Another, more likely, cause is that maybe you were driving (using your brakes normally) and drove through some high water or in a sudden heavy down pour of rain. The sudden cooling of the rotors will cause them to warp. I'm just under 30,000 miles and starting to notice a little warping on my rotors. My Honda Accord has had slightly warped rotors since 22,000 miles. The dealer wants to do what is called "turning" the rotors. They will actually grind off part of the surface of the rotor where the brake pads touch the rotor to make it perfectly flat. Your other option would be to replace the rotors. No matter where you go, you will probably need to have this done.
Now for the tires. The tires could have worn unevenly for a number of reasons. Poor alignment is a main cause and is probably at least partly to blame for your tire wear. The other issue is that the Pathfinder just eats tires, regardless of proper alignment. I had to have my tires replaced at about 28,000 miles. I kept them balanced and aligned. As far as the vibration is concerned, I have only found a couple of places that can balance the tires on my Pathfinder. The one thing that all of those places have in common is the balance machine they use: a Hunter GSP 9700. If you go to this website: http://www.gsp9700.com/pub/features/
click on "Locate a GSP 9700" to find a shop in your area that has one of these machines. Even the Nissan place couldn't balance my tires in several tries, so they sent my truck to one of these places because the Nissan Technical Service Bulletin told them to.
Good luck with your truck. You will really enjoy it again when you get this taken care of.