Complex sentence: Gernsback took the opportunity to sell items such as buttons and insignia, and it was undoubtedly a profitable enterprise for him as well as a good source of publicity, but it was ultimately more important in becoming one of the foundations of science fiction fandom.
Split into simpler sentences: Gernsback took the opportunity to sell items such as buttons and insignia, and it was undoubtedly a profitable enterprise for him as well as a good source of publicity. It was ultimately more important in becoming one of the foundations of science fiction fandom.