So have found 4 individuals with composite decking on 16" centers and all report no problems. One of these decks is over 10 years old.

I'll call a few manufacturers over the next few days and find out why installers are doing overkill based on their recommendations.

I'd be willing to consider a deck rebuild if the quotes I'd gotten hadnt of been 1/3 to 1/2 of what I paid for my first house.