When I was younger, it seemed like I needed to upgrade my computer constantly. Before college, and before my professional career started, the only aspect of my computing experience was at home. It makes sense that it was more important then. For a time, every year or two it seemed like it was a must. (From the 486 (DX4 baby!) to Pentium 166 to Pentium II to PIII to Pentium IV days).
I'm not sure if it just felt like it happened quickly, or if it really did. At the moment I'm not feeling like firing up wikipedia.
After a certain point, it seems like it became less important. Once I spent 8-10 hours a day on a PC at work, I no longer needed to do this at home. Somewhere along the line, though, something was lost. It's hard to be enthusiastic about a work machine. Sure, you want it to be fast and not get in your way, but at the end of the day, it's just not the same.
I went from 1-2 years between machine upgrades to 4 years - and I barely cared. There's still something special about doing it yourself, though, so this summer I finally upgraded from an Athlon X2 4200+ to a Core i5. That's not the whole story, but it will suffice for now.
The point is - building out a new PC, finding out all of the various motherboard pros and cons (and quirks!), selecting the other components, building it - it's been invigorating. The experience has really renewed my interest in experimentation at home. I want to try new operating systems again. I want to try X, Y, etc. It's interesting to see how things have changed, and how they haven't (You STILL end up staying up all night to setup that new machine - something ALWAYS doesn't go right). That Is The Law.
I actually enjoy using a desktop again. With Windows 7, I'll actually reinstall my OS again for the first time in a long while. (well, I've been reinstalling since Beta 1 came out) The list goes on.
I find myself reading articles late into the night, reading books, feverishly seeking more knowledge. I am excited about computers at home again.
You don't need to splurge for the latest - nowadays, hardware is cheaper than it has ever been. When I got my first 4 megs of RAM, it was $32 a megabyte! Now 4GB of DDR3 is $100. Dual and quad core CPUs are more affordable than ever. I am amazed at how lucky we as enthusiasts are these days :)
When's the last time you've upgraded? When's the last time you built a machine yourself? You may find it's a very rewarding experience. Build a file server. Build a box just to experiment with spare parts on ebay. Or use a virtual machine with a new operating system. Experiment!