I think they're amazingly over priced now but - it a situation like yours where you have a child who doesn't handle the crowds - it may be worth a one-time splurge. I recommend the one where you get to be in the garden as opposed to where you watch from the terrace.My 12 yr old is crowd averse and anxious, thinking this might be a god option to see fireworks/shows without worrying about being crowded. Is it worth it?
Another option - which we did for the very first time after 20 years of going to the parks - is to watch the fireworks from behind the castle. You don't get the projections but great view of the fireworks and wide open places to watch and sit.