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It doesn't directly improve the brightness. However, if you have the bunching problem, and are turning down the brightness and contrast to mitigate it, then doing this fix will allow you to run at higher brightness and contrast and still have a very nice picture.
The reason this took me several years to figure out is because you would think that if the vertical deflection is working fine at low brightness, then the caps must be doing their job OK. Since the problem was occuring only at high brightness, I was assuming that somehow the bright spots in the picture were causing HV collapse or something like that. I don't really understand why this fix works, but it sure does. I can't get over how good this set looks now.
Another thing that prevents a more direct troubleshooting of this problem is that one would normally want to probe the deflection signals right at the CRT to see if there is anything funny about the signal on a scope. But you can't measure those point with a scope because of the HV. If you probe on the low voltage side of the caps, you don't see anything really amiss.
We've known for many years that ceramic caps don't work in this application. I wonder if I cut open one of the latest .005 uF ASC tubular caps, I'll find a little ceramic cap inside? Just kidding, but it does seem to work a little like a ceramic!
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