I build my systems with at least a 5 year service life. If they last longer great, and if not then I need to do better. Our server is three years old. Had it not been for the dirty power that it is fed I would have never had the side off. In a year and a half it turns five, and at a cost of $400 per year for the benefit it has given it has done well. and might continue to do well for another few years.
Hey thats what I build computers for.
I usually make it last at least 4-5 years each
However, I look for the parts with the best cost / benefit ratio.
Thats how I rate my items and sometimes you have to spend a little more to make it last extra longer.
Like for example, people dont like to spend money on PSUs.
However, if your PSU (whether quality or non quality) is worked 85 percent or above constantly, then it will fail you a lot quicker than if you have a lot more headroom.
I am not saying go all out on your parts, but I am saying that you can def. get more reliable and better parts for $40 more and you can even save in some areas.