Re-reading the original text, it sounds like they just hoard more pearls because they are easier to aquire in their domain.
How about Standard coins; triple standard goods (all gems are pearls); standard items?
I still think we need more than that. An adult pearl dragon has H, U, while a great wyrm has H, U*4.
Type H:
5-30 1,000s of copper pieces: 25%
1-100 1,000s of silver pieces: 40%
10-40 1,000s of electrum pieces: 40%
10-60 1,000s of gold pieces: 55%
5-50 100s of platinum pieces: 25%
1-100 gems: 50%
10-40 jewelry: 50%
Maps or Magic Items: Any 4 plus 1 potion & 1 scroll: 15%
Type U:
10-80 gems: 90%
5-30 jewelry: 80%
Maps or Magic Items: 1 of each magic excluding potions & scrolls: 70%
Comparing those to the 2nd edition MM dragons that's pretty good. The Black and Brass Dragons just have type H as adults and H*3 as great wyrms, so a pearl dragon typically has the same coins as an adult than a Brass or Black's hoard, but more gems, jewelery & magic, while as a great wyrm it typically has less coinage but a lot more pearls, jewelery and magic.
Both Black and Brass Dragons have triple standard treasure in 3E, so I feel the Pearl should too.
The CR looks fantastic! Nice work.
Thankee kindly.
Level Adjustment: Wyrmling +2; very young +3; young +4; juvenile +4; others —?
That looks reasonable.