That reminds me about special care for Henle books. Even if you buy the paperbound books, they are quite expensive but are generally worth the money. They are well-informed, scholarly, and, most importantly, very clean editions. Therefore you will want to protect your investment in one way or another. Henle sells vinyl covers that are specifically sized to fit their paperbound books (all sizes except horizontal books). I have several of them and I swear by them. They keep the book clean, the cover stays that attractive shade of dark blue, and it protects them from damage. They are $3 each, pretty costly, so I only buy them for the larger books which are more likely to take a beating (entire collections of Sonatas, for instance). Another option is to protect the covers with a special clear tape that is used to cover books.
I myself haven't been around for 20 years, so I can't say whether or not mine will last that long. I can tell you that my teacher's Henle editions, which are well over 20 years old, are in great shape. She doesn't bother with the covers, but she does transport them in plastic bags when she leaves the house. I would assume that if you display a good degree of effort in trying to maintain the books, they will hold up nicely.
Topic: Henle - Paperbound vs. Clothbound???