Do you guys that had all the paste dry up by any chance use yours vertically? I would also add that the paste they use might appear dry when cold but when heated it becomes softer, hence why over time it can sag when the console is kept on its side.
I personally don't reccommend most people change the thermal paste, I would advise you open it up and clean the fans properly but don't seperate the cooling as it can induce a YLOD if you're not careful. If you do that then you'll probably find it lowers the fan speed sufficiently anyway.
For people that have more knowledge then the ultimate solution is obivously to change the thermal paste above and below the spreader plate. I'd advise a silicon based paste or one of the Artic Silver chipset compounds, basically something non electroconductive.