The difference between a truly good quality filter of the type that MichealJ and I use and ordinary filters is demonstrated in this
multipage comparison of a Tiffen and a Hoya.
Yawn.
Yes, this is the expected result when you test the filters under intentionally extremely high dynamic range conditions. Note that it compares
only dynamic range, but not resolution. However it gives me no way of determining what the actual dynamic range is (for instance, the white surround in the first image is saturated) so I have no idea if it is relevant to photography in the real world. He doesn't even say if his exposures were consistent within each set of images (I'm guessing that they probably were).
So the study says that multi-coated is better than uncoated, but it does not show that you need anything better than uncoated in most real world pics...
If you want to take lots of pictures into the sun, by all means get a multicoated filter (or just take the filter off). FWIW, I learned long ago to shade my lens (if possible) when there is sun on the lens... (A good idea no matter what kind of filter you use.)
One of my drafts of an earlier post included comments to the effect that the better coatings would primarily be useful under high dynamic range conditions. (This was hinted at by my notes on the strength of the reflection off the front surface of the lens.)
One of my sets of test images includes a white spot in direct sunlight and a dark object in fairly deep shade--under normal viewing conditions either image is fine. The difference is only noticeable in directed comparison. Also, after I took the pictures I noticed that the filter was somewhat dirty and needed cleaning, so I cannot tell if the effect was due to the dirt or reflections from the filter. The ISO was also 400 which was too high for measuring dynamic range. So this test shows that the effect is at most minor for a normal dynamic range image--it may be less for a clean filter.
Keeping your lens and filter clean is also very important in high-dynamic range situations--scatter off dirt and smudges can overwhelm the darker sections of the image.
I once dinged a $100 Hoya and was quite relieved to have the damage occur to the filter and not the Nikkor lens behind it that's worth ten times that.
I'll bet a $20 filter would have protected your lens just as well...
My fundamental point is that a buyer has 3 basic grades of filter at 3 different price points. The primary difference between the grades is the anti-reflection coatings which perform differently under high dynamic range conditions, but all should perform reasonably well under normal dynamic range conditions. All grades generally have the same resolution and all will protect your lens.
Doug