When you say mutimedia production/editing, I assume you mean that you are mostly working with video and other types of similar material, using programs like Adobe Premiere, Avid, or Hollywood Video (the program, not the movie rental store). If that is the case, then no, you will not see any difference whatsoever by upgrading your video card. The type of work you do relies on 2D performance and does not make use of the 3D graphics capabilities of modern video cards.
If you need a boost in 2D performance, I would take a look at ATI's FireMV (not to be confused with ForeGL) cards. They are specifically designed for 2D applications and have no 3D accelleration at all.
However, if you are using programs like LightWave, 3Ds Max, Maya, or something similar in your work, then yes, 3D modeling does make use of 3D graphics capability, and you may see an improvement depending on the work you do.
