Actually, most people go up several inches at a time. The diameter of the mirror has doubled, but the light gathering has quadrupled. To place it in perspective, if you have a small telescope, even a relatively minor increase in aperture will yield notable results. If you re already in the light bucket category, there are more factors to weigh in deciding on the value of a larger scope. My most vivid recollection in moving from a 6 scope to an 8 was that globular clusters were much more dramatically resolved.
Aperture certainly is only one of the many considerations in a move to a larger scope.
But it becomes the item of overwhelming importance to most people.