It would be interesting for you to say more about 'easily see use cases for more "muscle"'. I was under the impression that one of the challenges that PC vendors were facing is that laptops and PCs are 'good enough' for more and more of the computer marketplace and so they were unable to depend on 'upgrade' revenue as the components got more capable.
I don't doubt that there are folks that can use infinite amounts of computer power, but if they become so specialized perhaps it will shift the market around again.
One common scenario are the browsers. Imagine websites with real 3D model e.g. nike.com with a modeled shoe. Browsers are becoming an application platform and to deliver rich client style UI, it takes juice.
Video editing is becoming more and more common place with cheap digital video cameras and the ones on camera phones.
I agree that the upgrade cycle may become longer, but to me it seems like there is a market for more CPU power on the desktops. I think there is some normal fluctuation where you improve one or more corners of the industry at a time.
I don't doubt that there are folks that can use infinite amounts of computer power, but if they become so specialized perhaps it will shift the market around again.