I agree. If the the scope has a stray light problem, a sunshade will usually help reduce the glare and increase image contrast. Glare is usually worse for high mag scopes (that is, usually worse for a 6-24x than a 2.5-10x, for example), and gets worse as the magnification is increased. Some brands have much lower glare than others.
In this area, you tend to get what you pay for, although there are exceptions, both good and bad. Good scopes will usually have extra "glare stops" and ultra-low reflectance black coatings inside the scope. It's often the lack of glare that makes a high quality scope have such a "clear" image.
Whether or not you need a sunshade depends somewhat on the glare performance without one. To test for stray light problems, I usually look at dark objects with bright light in the upper half of the image, or just outside the field of view. Overcast sky during the day or a street lamp at night are good sources of bright light. Then I vary the magnification from one limit to the other.
If the glare washes out or obscures the image at high magnification, I try it again with the sunshade on. Sometimes, even a sunshade isn't enough to solve a bad glare problem.