Not missing anything. And not really an answerable question as EVERY camp and side hike affords a special experience.
The known attractions (Silver Grotto, Redwall Cavern, Little C, Tapeats/Thunder/Deer, Matkat, Elves, Havasu, Lava, etc.) are known attractions because they are over-the-top experiences. But all of the lesser known side canyons are worth exploring, so make sure to plan for a layover per week at the least and to plan a couple camps per week that you have never been to or heard about.
Most importantly, relish and plan for the lack of traffic, there will be stretches of days without seeing others. It will be busy at Tapeats/Deer Creek and Havasu, so discuss planned camps with other trips in those areas for a few days leading up to them. But you will find much solitude.
Exploration is the operative word.