I'm far from being an expert on the issue, but I would use metrics based on fresh water tables and usage to gauge further hotel or even housing, development.  I'm not sure if these metrics are in zoning regulations, but if not, they should be.

Other metrics might be sewerage and trash output limitations.

I'm quite sure these would help manage tourism growth.  But the key question is what other industry could flourish in Hawaii?  I would think aquaculture, i.e. seafood farming, but that hasn't taken hold, for whatever reason, either cost, regulation, technology, etc.