I used to build all my PCs, but these days I only use laptops. Bulding my own desktops was fun when I was a kid, but now I’m just too lazy to bother.
As for CPU speed I never notice much difference unless I play games (and then, bus speed and graphics card is just as important). I honestly can’t say I have noticed any significant difference in compile times between my old Pentium 4 2.4GHz and either of the newer Core 2 Duo laptops I use now. My old system couldn’t play HD-quality video very well though. In my experience, CPU power is less significant if you have plenty of RAM, a fast hard drive and a fast graphics card.
Personally I think CPU upgrading is much overrated. Of all the PCs I have buildt over the years, I only once upgraded the CPU (from a Pentium 2 350MHz to Pentium 3 600MHz, since I got the CPU for free from my brother). I also know very few other people who actually did upgrade their CPU, ever (they upgraded plenty of other stuff, just not the CPU). Nine out of ten times when upgrading a system I have to get a new motherboard (and RAM) as well, because the CPU socket has changed in the meantime, or the motherboard is not compatible with the current bus architecture.
When it comes to hard drives I always prefer to have two. One for the OS and one for my data. It can give a nice performance boost in addition to making life a lot easier when reinstalling your OS.
I guess all of this really depends on how often you upgrade or replace your PC. For me, every three years has proven to be an adequate rate.
That being said, your setup looks rather sweet