Hi, I really enjoyed this book. I'd actually say that they should forget the production hell surrounding 'Ringworld' and instead make these books into a series of films.
To answer your question, I think the title works on several different levels. First, as part of a series - Fleet of Worlds, Destroyer of Worlds - then they had to come up with some kind of '.... of Worlds'. Secondly, I do think Sigmund, as an ARM is a 'juggler' with societies and local governments, and in his dealings with Beowulf Shaeffer. Thirdly, I think the Puppeteers, and specifically Nessus, are also 'jugglers of worlds' influencing the Birthright Lotteries, releasing the semiconductor virus, monopolising the spacecraft hull business with General Products and then suddenly leaving known space to an economic crash, generally manipulating both humans and kzinti for their own whims, and also by creating the human colony in the Fleet of Worlds without knowledge of their true origin.
The book contained text taken directly out of the short story 'At the Core' and yet showed everything in a completely different light. I like all the political intrigue and find the Puppeteers are a much more believable race now. I think the Kzinti and Puppeteers are the most well thought-out aliens in SF.