Very interesting. I can understand the arguements for them (shade, looks plain without them, etc.) and against them (fireworks, destroys forced perspective, etc.)
Maybe they could plant trees that are smaller then normal. Makes the place look nicer, adds some shade, doesn't block the fireworks, and you can enhance the force perspective of the castle.
One arguement against is rather interesting, that the roots from the trees could be cracking the infrastructure. That makes a lose-lose situation. Either cut down the trees to keep the buildings crack-free, or leave them up, and have people complain about how the place is falling apart.