The cost of a computer with useable, respectable performance and disk space is approaching commodity levels. But another basic aspect of the computer certainly has to be its arithmetic capability. In many applications, the usefulness of a computer does go up with its speed and size more than with their numbers. These models can be as complex and slow as you want and always are as complex-slow as tolerable. Many simulation programs now work in two dimensions.
Reality is infinitely complex.
All Class VII figures are estimates. Large scientific computers can do long sequences of arithmetic calculations cheaper. Supercomputer technology as well as PC technology will progress. The CRAY-1 is 7 year old technology. The advantages that you point out for the smaller computers are certainly valid.