Video cards off board graphics processing from the main CPU/memory to a set designated and specially designed for video processing.
If you don't use the features of a video card, then it generally won't have an effect on your system performance.
Since you don't run games or the alike, you'll likely not notice a difference. Where you might notice a difference is that certain features of certain programs won't run. Since computers are so powerful now, many software products employ eye candy to make the UI look better.
An example of this is Windows Vista Aero. It is my understanding that you need a capable video card to run the Aero effects. It is certainly possible that the integrated video card can support this but the processing load would be put on your main processor. This would have an effect on your computer performance, however most of the time your processor is likely not utilized anyway. So, it will appear to have no affect.
Ultimately, if your computer is working to your satisfaction, I'd not bother updating it. I still believe that most people will find more bang-for-their-buck in maxing out their system memory over other upgrades.