Sorry, I would not put a dime more into that machine. Instead consider building your own computer. If you like the current case, keep it plus any DVD drives. For boot, put in a SSD in the 100GB range to house Windows 7 64bit, all applications, and all the /user files. I would replace any HDs with a pair of 2TB SATA II 7200rpm HDs in RAID 1 configuration. When Windows is installed on the SSD, drag all the individual user folders (that each have My Music, My Pictures...etc.) from the SSD to the RAID pair. Personally I would go with an MSI or ASUS motherboard for an AMD x6 CPU. While it will not be as fast as a top Intel CPU....it will not cost a fortune either. 
If you are not gaming, go with a the most powerful video board that does NOT require a serperate power connection. That will give you enough graphics capability to do all but the most demanding gaming.
The one thing the above set...no native USB 3 header support yet on most motherboards. You can find lots of motherboards with USB 3 ports on the back...but not with headers that allow for any USB 3 connectors on the front of the case. So you need to think about how important having USB 3 on the front of the case will be for you. This spring we will start to see USB 3 ports on cases...and USB 3 headers on motherboards. So if USB 3 is hot for you.....save your money and wait for a few months until the USB 3 cases (or parts that allow you to replace USB 2 ports on the front of the case with USB 3 ports) and most importantly...USB 3 headers on the motherboards.
Some folks shy away from computer building. I find it relatively straightforward. Remember that knowledge (around cameras, computers,..etc.) is power. Don't let a high school gamer at Best Buy "advise" you on a new machine. Instead spend the time to learn about your options. Use the time to build up a budget. Look for serious sales on HDs, SSDs, video boards....even keyboards (led backlite ones) and mice.
Enough of my ramble. I hope it helps.