The PSU and also the case (with it's filters / airflow) are the environment of the computer.
Any computer that matters never skimp. Not only will the PSU last longer, but you can do things like under-volt as the PSU will have better voltage ripple. Also better PSU's are more efficient so over time pay back towards the cost with energy savings.
Also on the subject of ripple, better PSU's are kinder on your computers electronics as any voltage spikes in the mains are handled better and less chance of getting onto the DC. I can assure you there are micro spikes that can happen many thousands of times a second on the mains where the mains voltage goes over +10%, so better quality PSU's are always helping to protect.
The other thing you should do, is try and get a PSU that's rated double the max wattage of the computer, especially do this if your building a workstation or server.