Yep, braille does wear down. That is part of the reason that braille is printed on cardstock instead of regular paper (that and that the embossing would tear the paper apart in the process).

Multiple volumes are produced per book to reduce bulkiness, but as you know, braille books are still pretty huge. For example, the first book of The Hunger Games, in braille, is produced in 2-3 volumes on 14x14 cardstock. This makes it less bulky to transport, and if it is stacked top to bottom, the braille won’t flatten as easily under the weight.

While most braille is a standardized size, jumbo braille does exist. The standard braille machine that most kid use is called a Perkins braille writer, and Perkins does put out a braille writer that embosses bigger dots. They aren’t, like, way bigger, by any means, but they can be great for someone who just isn’t getting that tactile feedback in their fingers. There is also plasticized “paper” that embosses really well and is great for sweaty fingers. I use that to make flashcards and reference sheets that will be used often because the braille doesn’t flatten or blow out.

One last thing, and this is just a general thing that I like to point out to people who are new to braille. When we look at braille guides that are meant for sighted folks, they may have enlarged braille in them, and I think there is a misconception that people who are sighted read braille by touch. We do not. We learn/read braille by sight; rarely does someone who is sighted read braille by touch (unless we are learning it because we have a visual impairment). So, there are some braille fonts out there that are easier for those of us who are sighted to read, and there are some that are meant more for conversion into various braille programs. That can have a hand in why different sizes appear and why some of the fonts look different. Just an FYI.

There are a few minor size variations, due to the medium. Braille on paper is almost always the same size, but I have heard of "jumbo braille", signs tend to feel a little bigger, Braille displays sometimes make the dots a little bigger or farther apart because of the difficulty of fitting all the parts into a smaller space. Generally, though, that's small enough a difference that it's hard to notice.

I haven't checked, but it does seem like line spacing is a slight bit different, depending on whether or not the Braille is embossed on both sides of the page. This might be less of a problem for machines, but it seems like the line spacing on my 3×5 card slate is a bit larger than on my 4-line 8.5" slate. The card slate is double-sided, and the other is single-sided.