I have 18 wheels with 285/60 Nitto Grappler tires. I have been to Moab the last 5 years and have not damaged any of my wheels. There is always a first time, but as of yet I haven't done it.
I say keep your 18s, don't buy the 16s, and use that money for a set of 285/60/ 18 Nittos.
Peace.
Tom