Have stayed in the Casitas many times. They're great but very outrageously priced (I seem to recall $1500+ for a two bedroom not in peak season). I can't imagine them upgrading anyone to them unless you're a close friend of the GM or some Hyatt big wig. The East Casitas have a better, more private location than the West Casitas.
We have stayed at this resort probably 20 times. I doubt there have been more than three times when there hasn't been some problem. Front Desk staff frequently seems too young and disinterested.
I keep hearing about the great breakfast in the Regency Club. I've never found it so special. Some granola, fruit, pastries and I seem to remember some cold cuts. I guess it's OK if you get it for free, but I wouldn't pay to upgrade to the Regency Club to get it.
Not all rooms at the resort are equal. Many of them face a busy and noisy entrance or the noisy Fountain Court (when they have live music late at night). Maybe only 25 or so face the beautiful pools.