Heat does degrade components over time, however since air cooling will keep your components running just fine long past the point that they become obsolete the point is moot.
Yep. I don't think it's really an issue. If you get solid parts, you should have a system that will last longer than your PC.
Additionally, you should be concerned that with less fans (assuming you are wcing for silence) the components on your board (voltage regulators, etc) are seeing less air flow over them, which might even... shorten the life of the components!