Guess what I just found.
10.62.
I looked up how they calculate rarity and it’s I think a good system, but not what I expected.
My first thought, and what they originally did, was that rarity was simply an index of how many of that aircraft type exist.
Instead, it’s really a ranking how many hours a given type flew in the look back window. So that’s my some of the kit planes I’ve caught have higher rarity than the B-29. More of some of these high rarity kit planes exist, but they almost never fly. So in reality, they’re much harder to grab.
Instead of just looking at how many aircraft exist, we now base rarity on actual flight activity. The values in Season 1 are based on measurements from a 204 day period.
Here’s how it works:
For each aircraft model, we add up the total flight time of all its individual aircraft during the period.
We then normalize this total by dividing it by the length of the measurement window.
The result is what we call “Full-Time Equivalent Aircraft” (FTEA). An FTEA value of 1 means that, across the fleet, the aircraft type flew the equivalent of one aircraft operating non-stop for the entire period.
To turn this into a rarity score, we apply the formula:
Rarity = 7.5 – log(FTEA)
Examples
Boeing 737-800:
Across all aircraft of this type, the total flight time in the 204-day period was 292,568.95 days.
That equals 1,434.16 full-time equivalent aircraft.
Applying the formula gives:
7.5 – log(1434.16) = 0.23Cessna T303 Crusader:
Across all Crusaders, the total flight time was 185.55 days.
That equals 0.91 full-time equivalent aircraft.
Applying the formula gives:
7.5 – log(0.91) = 7.59
I had a colleague years ago who told me he collected airplane tail numbers. I was rendered temporarily speechless at this, but then asked him what he did with them. He said that he talks to other collectors and they trade them. More silence followed. The OP’s version sounds more complex.
I woke up super early this morning and actually used an entire 2-hour unlimited photos upgrade for the first time. Two hours is a long time to stare at your phone catching planes, but by the time I earned my 150 coins back I still had an hour and fifteen minutes left… I ended up 250 coins ahead, and got my first orange cyber card! Overall, I would say the 2-hour upgrade is worth it, but I couldn’t possibly stand to do it more than once a month or so.
We on the Dope have our own weird little collection going:
2-1/2 years, 3300 posts about custom license plate spotting. What are we thinking? 
And it’s not even the first thread on this topic. But definitely the one with the most staying power.
Interestingly, the ancient threads died quickly. The last-decade’s threads lasted awhile before petering out. This one will probably live for the rest of the board’s lifetime. Is the difference that custom plates are more common now or that we’ve turned into boring geezers with little else to occupy our minds or days?
I have to relearn how to use the SDMB… I think I’ve been replying to people’s posts, rather than just adding a comment to the thread. I’ve been gone a while.
There are two reply buttons. One at the lower right of each post. Clicking that creates a reply directly to that post(er), with a backlink in your post’s upper right connecting to their post.
The other reply button is farther down the page below the last post at the right of a row of similar buttons. That one replies to the thread.
Discourse sorta muddies matters when you post-reply to the post that’s directly above yours (IOW post-reply to the current last post in the thread).
In that case, Discourse internally knows the posts are connected, but your post’s display makes it look like you replied to the thread, not the immediately preceding post. Example: this post was created as a direct reply to your post, but there’s no backlink at my upper right. And yes, this particular Discourse quirk annoys many of our people.
So you may not be as confused as you think.