It's all relative...nothing is written in stone. If you own a modestly-priced (~ $250-$300) 36X scope, I'm betting the glass quality of a Nightforce NXS 12-42x56 scope would absolutely blow it away to most people's eyes. But at the next level, the glass of a NF NXS 12-42x56 won't hold a candle to the quality of the glass in a NF Competition scope. Many such "relative" comparisons can be made amongst commonly available scopes in today's market. However, the better the features, typically the greater the cost; and at the highest end of the scale, extra bells and whistles will likely far exceed the cost of improvements/differences that distinguish low to medium-priced scopes.
The real question is where does the lower cutoff for "minimum acceptable" clarity fall? The answer is that it depends to some extent on the individuals eyes and preferences. Certainly, it is highly desirable to have some minimum level of glass quality such that you're not losing points that are directly attributable to poor glass quality. But past a certain point, the actual return on your investment will go south in a hurry. I would also point out that there are other scope features such as turret function/repeatability, and having a reticle you like that doesn't move once set, are likely to be equally important as the quality of the glass. It is generally a good idea to buy the best glass you can afford - a scope that meets some minimum level of performance and functionality such that it will not be the limiting factor in your game.
By analogy, it is also theoretically possible to "overscope" a given rifle setup. For example, you will probably not get the most for your money by putting a $3500+ March scope on top of a bone-stock low-end Remy 700 factory rifle. Once purchased, you will always have the scope, so your money won't be lost, and you can always sell a good scope or use it on a different rifle. But perhaps someone just starting out with a very modest rifle setup would be wiser to get a little more for their money by going with a slightly less expensive scope, and spending a little more on reloading equipment and supplies.
In the end, my suggestion is usually to buy the best you can afford, whatever that may be, with the following caveat: if the best you can afford at some given point in time will be a limiting factor, you're probably better off saving your money until you can afford to buy some better that won't be limiting. Money spent on a tool that doesn't meet the minimum acceptable criteria is money wasted.
. There are top quality scopes with fully multi coated lenses
