Your current system is still pretty decent for video editing at 1080/60p footage... http://www.anandtech.com/bench/CPU/28
. To improve upon your current system, your best bang for the buck would be to upgrade to a Phenom II X6 (1055T or 1090T (my recommendation)) CPU after flashing your BIOS to 2005 or higher. Your other option would be going with the Intel Core i7-930 but you are talking almost a completely new system.
Your other components still meet the requirements for HD video editing. After the CPU upgrade, you can look to add a SSD down the road to complete the upgrade.