What's the significance of something like baptismal regeneration or the perpetual virginity of Mary?

I've been posting a lot on both subjects lately, but people often dismiss such issues as insignificant. A recent post I wrote about baptismal regeneration focused on one of the reasons why that issue is important. And I linked another post that discusses thirteen problems with baptismal regeneration, which provides other reasons for considering the subject significant.

Another reason for thinking more highly of these issues is how they're connected to other topics. Whatever significance the perpetual virginity of Mary has when considered in isolation, it takes on more importance when you consider how it has implications for claims about church infallibility, papal authority, the nature of extrabiblical tradition, and so on. Similarly, something like whether Mary was assumed to heaven doesn't have a lot of significance in isolation, but it becomes more significant when it's attached to other things, like papal infallibility and the infallibility of one institution or another.

There's also the issue of Biblical precedent. Many of the arguments used to underestimate the significance of baptismal regeneration could also have been used to underestimate the significance of adding circumcision as a means of justification, for example. Yet, the apostles treated the adding of circumcision as a major issue. (They also applied that reasoning more broadly, since they refer at times to the broader subject of adding "works", "conditions", etc. They didn't think circumcision was the only thing that couldn't be added.) As I've argued elsewhere, Peter probably was criticizing the concept of baptismal regeneration in 1 Peter 3, which is why he framed things so similarly to how Josephus did when addressing that sort of misconception of baptism in the context of John the Baptist.

And an issue doesn't need to have maximal significance in order to have some. I do a lot of work on Christmas issues. There's some value to knowing whether Jesus had siblings, the nature of his relationships with those siblings, and so forth. Though those aren't foundational issues or highly significant in some other way, they do have some significance. It's the type of information people often look into when studying the background of any historical figure, writing biographies, etc. It's information that tells you something about how the person's character was shaped, what experiences he had in life, how reliable certain people are (like siblings) as witnesses of his life, and so on.

I'm not trying to be exhaustive. These are just some examples of reasons why these issues are important.