To me there's two perspectives on this one:
1) What features are you looking for that you don't have now? Looks like that upgrade will cost you $499 from Sweetwater. If it's worth that much to you to be current then go for it.
2) Unfortunately you'll probably have to upgrade sooner or later if you want to stay working with ProTools. Something will push you whether it's a new computer or interface or whatever. Avid seems to have adopted a pricing strategy for upgrades that enables them to get nearly the same amount of money from you whether you skipped a version or not. What I mean is that if an upgrade from A to B cost $250 and an upgrade from B to C cost $250 Avid is making sure that an upgrade from A to C costs about $500. So you might as well upgrade now and use the new software for a couple years since you're gonna have to pay for it eventually anyway.