Atrophy manifests in different ways for different people. Some people experience dryness, other people actually experience an increase in secretions on T. I think for most people, the consistency changes. I've heard people say it gets more watery.
From the research I've done, it seems established that yes, you are at a slightly higher risk of infections down there on T - partly due to the symptoms of atrophy, partly because the pH changes slightly. I don't know how much...er, "moistness" will affect that. The skin inside becomes more fragile, meaning its more likely to tear and open the way to infection (including STIs).
It's something to be aware of, but not something to worry about too much. Like you say, if people were having major problems, they would be talking about it.
And if you do have problems down there, you can get oestrogen cream/pills you apply to the canal that will pretty much solve the problem (though you may need multiple courses over your lifetime). Because the treatment is targeted, it won't raise the E levels in your blood enough to cause any problems/be clinically significant.
Basically, any issues you have are likely to be minor, and if they're not, there is effective treatment available.
