Yup, sadly too many people ignore this. You also should re-apply the fresh one at lest once a year. If you ask most of the people they have their computer +5 years and have never done it. About the thermal paste or grease... definitely go for high-end stuff. It will make a notable improvements and helps to protect your equipment. Right now Iam experimenting with rather interesting compound. It is called nanodiamond thermal grease (here). Its based on nano-particles so it fills every space even down to nano-level.
