most thermal paste especially factory rubbish degrades over time and becomes hard but 11 months is not a long time for it.
it's purpose is to fill the gap between a thing making heat to the thing radiating it. air, ie and air gap between the two, transfers heat worse than the paste so you use it to ensure there are no air pockets between the two surfaces.
the smaller the distance between the two surfaces the better but do not worry about surface finishes on either for the most part, most CPUs are not flat anyway (convex).
in an ideal world removing all the old paste, cleaning the surface with alcohol / CPU cleaner kit etc should make the new thermal paste perform better / apply better but really the real world performance difference between most aftermarket thermal pastes is small. mounting your cooler poorly will do a lot more to give you bad cooling performance.
ps please note some thermal pastes can be conductive so they are fine on the heatspreader of a CPU / GPU but you could cause a short if you get it over the surrounding SMD components so due care and attention should be taken when dealing with it.
Ed