If you rebuild your PC on a regular basis....say upgrade every year to year and a half. And you have nothing to lose go ahead and overclock. If you are going for huge gains...frs'...speed etc. don't count on it. Usually gains are minimal at best. CPUs and the like are desgned to run within parameters. Naturally if you stretch them a price will be paid. The components overclocked will have a shorter lifespan without a doubt no matter how you cool them.
Best thing I would advise is always build/buy a PC that doesn't have to be overclocked. You'll end up happier in the long run with fewer headaches,PC downtime, and you'll save money and time.
Overclocking for a boost in FR is most times useless. An increase of 5 to 10 is not worth it. FRs' are dependant on monitor refresh rates. You're not going to get higher frame rates then your monitors maximum refresh rate anyway.