Why I won't be buying new desktop parts

Based on my normal computer cycle, I should have upgraded my desktop in late 2008, early 2009, but haven't. As a computer approaching 5 years old, my desktop is aged, if not obsolete. There are some things that it chokes on, mainly any computer game released after 2005, and playing back certain poorly-compressed HD video. Looking at the parts I would buy to make it new and fancy again, they are relatively cheap (in computer terms): ~ $600 for new motherboard, processor, and RAM. I could probably make do with spending half as much if I were planning to replace it sooner (i.e. in 3 years instead of another 5).

Still, my computer is fine as-is (i.e. until something breaks), I don't need a slightly shinier and fancier new monitor, and $600 (or even $300) goes a long way towards buying more Legos. :)