I'm interested in point 3 of your answer. Are there known cases of this? Which crypto wallet companies or devs have been caught collecting data?
If we are talking about the monetization of wallets, then collecting data for this is not enough. It means that they earn on the sale of this data. Here I have one more question: are there cases when ads were published for data sale of various crypto wallet users?
I don't know of any cases, although that doesn't mean they don't, and to be honest I would be surprised if they didn't. Since, a lot of companies out there unrelated to Bitcoin have been caught collecting data, and selling it. Even when it hasn't been publicly declared, if you go, and sign up to a bunch of companies with throwaway emails or using the
[email protected] method, you'll soon find out that the companies claiming not to sell your data are, because you'll suddenly over the next few weeks get a bunch of spam from random companies.
Although, there's probably not a lot that you can do, since the above method isn't exact proof, and wouldn't stand up in a court of law. So, while there might not be any cases to go on, that doesn't mean you should automatically trust them.
Only give your data to people, and companies you trust, and ideally you'll be able to count on two hands the amount of companies/people you trust. I can without a doubt in my mind say that altcoin wallets absolutely have been collecting data that you wasn't aware of, since there's a large amount of crap out there, which is quite openly a scam, so why wouldn't they abuse their user base via their wallet software too.
As for the main Bitcoin wallets, well most of them are open source, so you can verify it yourself. Basically, any closed sourced wallet software you shouldn't be using, and collecting your data would be the least of your concerns in that case.