Thermal paste is basically to fill in surface imperfections between the cpu and heat sink to create better contact.
Yes, it could affect the temperature if the paste is dry.
It will also effect the performance of it if you lift the heatsink after applying it.
Clean the CPU and heatsink with isopropyl and re apply a grain of cooked rice sized blob ontop of the CPU. Place the heatsink onto that with out lifting it at all. This will spread the paste around evenly.
My opty 165 came with a thermal pad too....i peeled it off, because it would just cancel out the paste, and personally i think paste works better for heat management.