I have to disagree with Willow about Compaq. As a fellow computer builder, I remember trying to upgrade my dad's Compaq was a nightmare. It had very few expansion slots, and the case was very difficult to get into. I build my own usually too, and my current desktop is an HP (who merged with Compaq.) It runs fine, and would be great if I didn't ever want to upgrade or expand it, but the case is really poorly designed. It can only accommodate one hard drive, which is mounted oddly, and there's not much room in there to manuever while upgrading. I can't even add an additional fan.
If you can buy the parts that are wearing out and keep your case, which you seem to like, I'd go that route - it's worked best for me historically. Even a motherboard and processor aren't too difficult to change if you've got experience building, and it seems you've got experience and knowledgable family available to help. I am so building my next computer from the motherboard up again.