The only reason to upgrade a PC is for gaming.
Sorry, but this argument is, for lack of polite term, bad. There are plenty of reason you can need a powerful rig that have nothing to do with gaming.
If your home computer is also your work computer, there are many jobs where you would need a 1000 or even 2000$ rig.
Even if it's not work and just a hobby the same applies.
3d, video, audio to a point, encoding, encrypting/decrypting, large data manipulation, server, development software (adobe, virtool, etc.)...
I've also seen a fair share of dev kits that require a powerful computer because they are badly coded and the extra power keeps them from crashing all the time.
Even watching movies requires a descent computer. Watching a Blueray disc requires something like a mid dual core with a descent graphic card, else you can see a loss of frames.