Big game hunting, I rearly use more then 11-12x and its PLENTY even for 1000 yard hunting on big game if your using a quality scope. Most of my shot opportunities are first and last 30 minutes of light so the really high power scopes are not as useful to me or needed in my opinion.
Varmint hunting, yes, higher power scopes in the 20x range are great and often needed.
I have taken three rockchucks at ranges over 2000 yards including one at 2370 yards which was the 2007 Varmint Hunters Longest Shot of the Year shot. All of these were made with a NF NXS 3.5-15x 50mm scope set on 15x. Was it PLENTY of mag power... It worked. At these ranges, on this size target is was marginal for sure but for big game at 1000 yards, it would have been MORE then enough.
I think we often get to caught up on high mag scopes and often if optical quality is good, you do not need as much mag power.