Who cares about long computer life? The thing will be obsolete junk in a year or two at most. Here in the swamp, computers rarely go more than 6 months or so without some kind of major upgrade/rebuild or total replacement. Everything here is for sale.
At the speed computer technology advances, you must surf or die. If you want to keep up at all, you gotta be constantly selling off parts or whole machines to (partially) pay for buying newer parts or machines.
If you keep anything too long, you can't even give it away. Don't get attached to that stuff. Sell it quickly, while it's still worth something, and buy new(er) parts.
It's best to have a crazy friend with too much money that likes to surf at the bleeding front edge of the wave. That way you can buy his used parts, which at that point will be still quite new and cool, but not stupidly expensive anymore. This is my situation
I've found that by selling stuff fairly soon, I can usually recover around 2/3 or better of the cost of newer, more advanced parts.
I used to leave my boxes on 24/7, but found that fans die prematurely and the box collects too much dust inside. These newer machines move a LOT of air thru the box to keep cool. Air comes with dust. You gotta open em up and clean em often.