99.99% of the time, a computer is basically idling waiting for user input. Some programs do involve heavy duty processing (graphics programs fall into this category, especially 3D rendering), but even those programs only do that kind of processing a fraction of the time. Going to a faster CPU will only allow the computer to wait faster. Little extra work will get done.

I've seen people who complain their computer is too slow when all they do is word processing and they don't even know how to type. Learning how to type would be the most effective speed up most people can do. Learning how to use keyboard short-cuts and how to make most efficient use of their programs is often more productive than going to a faster CPU.

There are some cases where going to a faster computer can be worthwhile. For example, if a system redraws a CAD drawing every time a change is made, then the user might have to spend a lot of time waiting between inputs. Most of the time, this just isn't the case. Most of the time, going to a computer 2x or 200x faster will have little impact on how long it takes to write a paper, update a spreadsheet, or manipulate a CAD drawing.