It depends on what you're doing with the computer. If you do a lot of video editing or even photo editing, it might be useful. In your case, half your RAM is being used for auxiliary functions by the OS, so I don't think you're someone who needs more RAM. At least not yet. Once that "Available" figure drops down to maybe 1GB or less on a regular basis, you can think about adding more RAM. Otherwise, I'd say it's probably a waste of money, not that it'd hurt anything adding more.