Agreed, you should be just fine unless gaming.
The only reason I can think of ATM for using a dedicated GPU for Video Rendering only, is the Hardware Accleration aspect.
ATI/AMD has AVIVIO and Nvidia has Pure Video. Both are esentially the same thing.
Having the GPU decode the video with these may give you a slightly overall better image.
But then again, the software you use for playback will have some affect as well.
To be fair, Im not sure how much of a difference that would be over the CPU integrated video, or if it would even be worth it to you.
If you decide to go with a dedicated card to decode Video, you do not need a very expensive one.