Running your components cooler will lead to a longer life, though probably not a huge difference if the temperature is slightly lower. For GPUs you will generally get a good lifespan out of them if you keep the temperature under 80 degrees celsius. Most GPUs can take temperatures higher than 80, but it will shorten the life of the card. Running at 100 degrees celsius or higher is about the point where you start damaging the card.
Admittedly lifespan may not be a huge issue for GPUs if one always wants to be on the cutting edge, or absolutely must run most or all games on maximum settings. Some of the more enthusiastic gamers will upgrade their graphics card every two years or so, and a video card should easily last that long, even if it is running on the hotter side.
Usually once a card gets to 4 years old it is generally considered obsolete, as it is likely to appear on or below the minimum system requirements for new titles, though the current lengthy console generation has changed that to an extent. A high end card from 4 years ago like an 8800GT can still run any title that's released, though not at ultra settings at 1080p.