I noticed that in your original post you mentioned that you already bought a case and a new video card. I don't typically suggest that people who want to build a gaming rig buy the video card first and then go and ask for suggestions / help on the forums about whether they should upgrade their PC.
IMO: While there aren't expiration dates on video cards (or any other PC hardware), video cards come to mind as one of the few components that could have one. If there is a chance that you can still return that video card (unopened, still have the receipt, bought local, etc...) I'd start by asking about that component first.
As for your question. As others have stated, I too agree that it depends on if your PC doesn't accomplish your typical tasks the way you want it to. Of course, if you have money burning a hole in your pocket, why not?!?
I'd like to point out that I think of two different PC upgrade methods:
1) Buy EVERYTHING new and get rid of practically every trace of the old PC.
2) Upgrade incrementally. Replace the things that will give you the biggest bang for your buck now, and replace the things that need replacing later, later.
A long time ago someone suggested that I buy really quality components in key areas and then just replace the other parts as they needed it. Sure enough, I've spent a large amount of money on my Monitor, Keyboard, Mouse, Case, and Speakers. I've also spent a bunch of money on my Video card, CPU, Memory, HD, etc... But, the point is, I really only 'interface' with the Monitor, Keyboard, Mouse, Speakers, and Case. Sure, the case is only when I turn the PC on or off and maybe to load a disc. But, the Keyboard, Mouse, and Monitor and needed in just about every interaction I do with the PC. I don't need speakers to surf the web, etc... But try doing anything without using your monitor, keyboard, and/or mouse!
I have a good friend who just doesn't listen to reason. He spent over 3 grand on rebuilding his PC maybe 2 - 3 years ago. He bought a pair of G-Force 295 Video cards (IIRC, they were the best available at the time). Then, he calls me AFTER he made the purchases. I told him that he likely would have been better off buying one card, and then another when the next new line of cards came out. Just a few months ago, he bought a pair of Titans (yeah, over $1200 to replace a pair of 295's). My point is, yeah, he didn't buy a whole new system (so he learned something). But, waiting that long to change out the video cards (and then going straight to SLI'd Titans) was a waste. He likely would have gotten much more enjoyment and value out of doing a incremental upgrade on the video cards in between. To make matters worse, he's still using a 1080P monitor with that beautiful set of Titans... Facepalm...
Good luck with whichever path you choose. Upgrades can be fun!