Unless you were standing in the tree hub, then I'd say you'd have trouble viewing Wishes, but with the photos of looking down Main Street, the trees don't even surpass the height of the castle's lowest spires! There's no way, even if they were still there that they would effect viewing Wishes from Main Street, where so many people watch it from, and the show almost 100% designed with Main Street in mind as its rather strange to watch it from Tomorrowland or Adventureland.
The trees added shade and gave a park-like setting to the hub, as they got bigger in the 80s and 90s, the trees starting to block out the Contemporary from Liberty Square.
The trees were a transition....you walked down Main Street, saw the castle, but the bottom of it was partly hidden behind trees...the prize was in sight, you just had to keep going toward, keeping walking, then into the hub, past the clearing in the trees and there it was, the castle towering over you.
:drevil: