Don't repeat platitudes, build a model. I.e., make up plausible numbers and actually do the math. You'll see that without making wildly ridiculous assumptions, it's just a net loss for Ford.
Or, may I guess, most of the people that buys Ford's cars does not work directly for Ford.
1) Tired workers make costly mistakes, often countering any extra production they may have made 2) Tired workers work more slowly 3) Tired workers miss opportunities to save time through better work methods
Reducing hours towards 32hours /week will usually net you more produtivity per week. Increasing past this will give you temporary improvements, but they won't last beyond a couple of weeks.
Not to mention - the more Ford pays per hour, the better the quality of the workers he attracts.
The profits might be spent on luxuries, the costs on materials. Once again it split up. Every time a small fraction goes to the government, or to Henry Ford.
His point is that he wants all business in America to be vibrant, not just his own (because his businesses would die if it weren't part of an ecosystem)