Looking to upgrade my old system.

Hey everyone. I'm looking to upgrade my old gaming system and I was wondering what input you guys would have (aka where can I get the most bang for buck?)

My current system can run new games like Dead Island with virtually no problems, I was just wanting to maybe start the upgrade process because I don't really have the money for a new build right now.

Here's my current specs:

Processor: Intel Core 2 Quad Q6600 2.40GHz

Motherboard: Intel DP35DP

GPU: GTX 250

OS: Windows 7 64 bit

If you think it's a wash and to just save and build new, I'm okay with that too. I just have to wait a few more months for an upgrade.