If you hold a US passport (or any passport that allows "visa free" entry on arrival) and you're not carrying prohibited meds, it should be pretty painless. There are some forms to complete. The line for immigration varies depending on the number of flights that have landed but you can often get from gate to arrivals hall in under 30 minutes. With a 9.5 hour layover I would say it's a no-brainer.

I don't think that's the case, unless you add status in a loyalty program to the left side of "so" in that equation.
I haven't been in that lounge recently but if memory serves, it has a buffet with hot food.