In what applications (is the question that will be asked of you in return)?
Have you tracked your memory usage? Does your hdd 'grind' a lot (heavy use of the PageFile)? On an avg night what do you have running (a game, 2 or 3 browswer windows + tabs, word processing, porn, movies paused/playing)?
The quick answer is yes with ram dirt cheap. But spending $0 is infinitly cheaper then spending even $1.