The better question for me is not the number of travel books I own, but the number of bookcases in which they are stored.
I browse through the travel section of bookstores often. The books I purchase are usually about areas to which I'll be cruising.
Most of our books, though, are purchased during our travels. For instance, when we were cruising the Norwegian Fjords last summer, we picked up a few history books on some of the towns we visited. We did the same thing when on a land tour to Tucson, Arizona last year.
Cruise books, particularly those on ocean liners and cruise ships, remain my favorite. I must have well over 50 of those.