I have a modified A7 and beginning a running review on what sort of difference it makes on legacy lenses.
https://www.pentaxforums.com/forums/76-non-pentax-cameras-canon-nikon-etc/300...stacks-up.html
At this point, its still early to conclude, but my current feelings are.
1. Not all lenses will see significant improvements
2. Wides, 24mm and wider, more likely affected by the thickness than longer FL.
3. There are tradeoffs (color temp, glass corrosion resistance, etc)
4. For the geek, thinner is probably less harm than thicker.
The following comment is based on stock A7 with many uwa.
Generally new uwa are better than old ones.
28mm and above, generally no issues.