I do the same thing whenever I have the opportunity. The FTC does have some resources, but a list of spoofed numbers doesn't do them any good (There's an article on www.consumerist.com several years ago, about their difficulties in chasing some of them). Following through on the call serves two purposes. 1) Keeping them busy, like you say here and 2) getting sufficient actionable information to help the FTC in their investigation.

Their business model is dependent upon uninterested people not answering, blocking, or not pressing '1'. Computers can call millions of people, but they only have actual people to talk to 1 to 2 dozen at a time. Break their model and Denial-Of-Service their agents by answering, talking to them, and wasting their time. Yes, it takes up your time now, but after they are bankrupted, everyone will benefit.