After a lot of improbable things happen the main thing you have evidence for is that the universe is large enough to have improbable things happen. This could happen in MWI, or it could just happen in an ordinary very large universe. Or it could happen in a simulation that focuses on special events, so if your event is special this is also something that gets more support, relative to a small universe.
But I don't at all see how such events give you evidence about what sort of large universe you live in. And I don't see how winning the lottery is remotely unlikely enough to kick in such considerations.
I don't see how the size of the universe makes any difference - isn't it only the density of weird events that matters?
In passing, I said:
And lo, CronoDAS said:
To which I replied:
There's a certain resemblance here - though not an actual analogy - to the strange position your friend ends up in, after you test the Quantum Theory of Immortality.
For those unfamiliar with QTI, it's a simple simultaneous test of many-worlds plus a particular interpretation of anthropic observer-selection effects: You put a gun to your head and wire up the trigger to a quantum coinflipper. After flipping a million coins, if the gun still hasn't gone off, you can be pretty sure of the simultaneous truth of MWI+QTI.
But what is your watching friend supposed to think? Though his predicament is perfectly predictable to you - that is, you expected before starting the experiment to see his confusion - from his perspective it is just a pure 100% unexplained miracle. What you have reason to believe and what he has reason to believe would now seem separated by an uncrossable gap, which no amount of explanation can bridge. This is the main plausible exception I know to Aumann's Agreement Theorem.
Pity those poor folk who actually win the lottery! If the hypothesis "this world is a holodeck" is normatively assigned a calibrated confidence well above 10-8, the lottery winner now has incommunicable good reason to believe they are in a holodeck. (I.e. to believe that the universe is such that most conscious observers observe ridiculously improbable positive events.)
It's a sad situation to be in - but don't worry: it will always happen to someone else, not you.