Here is what I do when building a PC:
Invest in the best case possible. This would include a "quiet" one but not so much for the quietness but that the quiet case will have better more durable materials, better and easier to replace fans (you want good fans as a failure will kill your hard drive very fast). Ideally this should be made of a heat dissipating material like aluminium. The case goes obsolete the slowest. I am still using a ten year old case for one of my computers and I see no reason why I cannot use it for another ten years (yet).
Next is the power supply. A good one is worth the investment because it also goes obsolete very slowly compared to other technology. Plus a high quality one will be more likely to protect the precious Hard Drive with your data from a power surge.
If you want basic writing and internet stuff then get a good motherboard but get a cheap one. Get one with what was a good processor two years ago and then use the savings to get as much RAM as possible. This will make replacement easier should it fail and the increased RAM will make the motherboard stay active and capable much longer than a default setting. Double the current default...like if 4GB ram is used on all laptops now, get 8GB or more for your desktop.
Hard drives are cheap now so get 4 of them. 2 for a RAID configuration that makes it so if 1 Hard drive fails the other hard drive takes its place. Have the third hard drive as the replacement ready for the RAID one and the fourth one used in a "USB toaster" for backup of data, like this:
http://www.amazon.com/Thermaltake-BlacX ... B001A4HAFSGet two backup cheap keyboards and two backup cheap mice too. One beer spill can be corrected in minutes if you have these on hand.