Same here, I finally upgraded a few weeks ago from a system that (at its core) was 5-6 years old. What finally got me to upgrade were the recommended system requirements for some of the newer games.
Assassin's Creed Unity -
CPU: Intel Core i7-3770 @ 3.4 GHz or AMD FX-8350 @ 4.0 GHz or better
CPU Speed: Info
RAM: 8 GB
Video Card: NVIDIA GeForce GTX 780 or AMD Radeon R9 290X (3 GB VRAM)
Free Disk Space: 50 GB
Star Citizen -
The Recommended system requirements are: i5 2500, i7 2600, 2700 or better with a GTX 670 or greater (DX 11 only).
And for a smooth experience at Maximum settings at 1080p, a R9 290x or GTX 780 will be required (a GTX 680/R9 280x will likely therefore achieve high comfortably). For a 4K experience, a pair of mid-high end cards (680/770 7970/280x or better) or a future high end card (GTX 1080 or R9 390x etc) will be required.
GTA V -
Processor: Intel Core i5 3470 @ 3.2GHZ (4 CPUs) / AMD X8 FX-8350 @ 4GHZ (8 CPUs)
Video Card: NVIDIA GTX 660 2GB / AMD HD7870 2GB
Sound Card: 100% DirectX 10 compatible
HDD Space: 65GB