1. Yes, the Flash Pass is absolutely worth it. It should be quite crowded. So, unless you enjoy waiting in lines, I enthusiastically recommend getting one. I'll be there on 9/1 with a friend, and plan on getting one.
2. You get an electronic unit (they used to be small, egg-shaped devices with screens, but I believe they are now similar to watches). You scroll through the list of rides (and corresponding reservation times) on the screen. You find the one you want and select it. When it's your time to ride, the unit buzzes to let you know. You go to the separate FP line, where an employee checks you in, and you walk right into the station (for the most part). At that point, you can reserve another ride (you can only have one reservation at a time).
3. Yes, the three tiers are distinct from each other. Regular Flash Pass doesn't reduce the wait time, but you don't actually have to wait in line. The gold level reduces your wait time by 50%. The platinum level reduces it by 90%, and you have the added bonus of getting two rides in a row (you get to stay in your seat when you return to the station). I believe, however, that this bonus is excludes the front and back rows of any coaster.
To elaborate on the wait times, the unit gives you reservation times based on your FP tier. Say that it's 1:00, and you want to ride Medusa, which has a 1 hour wait. If you have the regular level, the reservation time on the screen will be for 2:00. You reserve it, and go do other things in the park (don't have to wait in the physical line). At 2:00, the unit will buzz, and you can go to Medusa, the employee in the station will check you in and clear out the reservation, and you head right into the station to pick your desired row. If you have the gold level, the reservation time will say 1:30 (cutting your virtual wait time in half). If you get the platinum level, the reservation will say 1:06 (cutting your wait time by 90%).
I find that for SFDK, which typically doesn't get waits longer than 1 hour, the gold level will suffice. If you make your reservation immediately upon checking into a ride (where the employee clears your previous reservation), by the time you wait in the station, ride the ride, and walk to the next ride, it's typically time for your next reservation.
I hope this helps. Enjoy your day.
Hey thanks for the information, this definitely helps. I was really mulling over going with the gold or platinum, so this was definitely helpful.