High CPU temps will make your system unstable. Cool temps usually come hand in hand. It is also more difficult to have a cool CPU with high system temps.
What I am personally most concerned with now is the temperatures of my hard drives. Hard drives seem to be much more susceptible to heat now compared to years ago. Also, if a HD dies it may be difficult if not impossible to replace. Your CPU and other components are easier to replace and running your system hot may decrease the life of your CPU from 10 years to 5 years, but is that really all that important?