Double Duty Thank You

A guy just held the door for me. It wasn't early enough to be awkward. If someone holds the door and you're 15 steps away, it's just awkward, and you don't even want to say thank you, because chances are you just jogged to the door. It's almost like you're doing them a favor. They're in the mood to do something nice, and to help them, you jog.

BUT, it was early enough to warrant two thanks. It was just barely too late for the first thank you to be a half smile*. My face didn't have time to react, and trying to make eye contact and maintain in time to half smile* at that distance would have been embarrassing. So instead I said "thanks" two steps before reaching the actual doorway. And since he insisted on doing a really good job of holding it, that is, waiting till I was all the way through to let go, I thanked him a second time. Just as I passed through the doorway I said, "preciate it." I was too rushed to keep the "I a-".

I think it only needed one gesture of thanks, but it felt like too much silence. I mean, the guy obviously thought it out. It was on the brink of being too early to hold the door, and right in the 3-step gap where not holding the door would be excusable and holding it would be thoughtful. (Note: I was 2 steps before the final decision line, past which not holding the door would be rude.)

Anyway, whether or not it was required, I belive my response will encourage him to continue his thoughtfulness and ultimately, make the universe a better place.
Segue to the discussion point:If there are two doors in a row and you are following someone (this happens at a lot of restaurants), are you supposed to thank both times? If only once, when? Is too much thanking even meaningful at all, and if one is going to use multiple thanks, should they be different?

What if A holds door 1 for B. B passes A and holds door 2 for A. B obviously thanks A at door 1. Does A thank B at 2? Do they shake hands and show each other family pictures?

*half smile: The half smile is often performed in conjunction with a head nod. It signifies, I recognize your existance, and I may or may not care. In my opinion, recognizing is nicer than not. If done after someone holds the door for you, it can safely be interpreted as "thank you." It's not a real smile, and I believe it takes less than half the energy of a real smile. If a male gives another male, who is familiar but not on a conversational basis, a real smile he is either very gay or very happy. This is allowed, but I would feel awkward doing or receiving this.

If a male does the above while holding the door for another male, then replies to the second male's "thanks" with a emphatic "shhhuuurre!", he is either definitely very gay, definitely very strange, or definitely a cartoon character.