Blah blah blah, I don't understand the concept of opportunity cost therefore people should ignore the expense of replacing equipment that is a little wasteful of a resource that is currently very cheap.
You don't need a 1kWe monster for day-to-day tasks, but if you want to have one for special tasks (computer game playing might be a hobby of yours, and is certainly less energy intensive than other hobbies you might have. Auto racing, for example), it might not make sense to also have an 80W computer for general use.
To pay off a $300, 80W machine in this scenario, at US prices you'd need to have like 3000 hours of low-intensity computing tasks. That's the break-even point assuming you're comparing it to a 1kWe monstrosity. If your gaming machine is closer to 500W (still pretty beefy, I'd think, and plenty of quad cores will fit into a balanced machine with that kind of power usage. At least a high mid-range device), it's closer to 6000 hours for break-even.
And it gets worse. It's unlikely that your 1kW monster is actually going to use the full power of all of its components when doing the general tasks, further eroding the advantages the smaller machine has.