"I would never wanna belong to any club that would have someone like me for a member."
-Woody Allen who attributed it to both Groucho Marx and Freud
Have you ever met someone who said: "I only go to conferences if they pay me to speak." It is undoubtedly not as common as getting to speak for free, and there are many conferences that charge the speakers for access to the audience. Simply, if you draw enough people, you can get paid to speak at a conference.
There is another similar thing going on at conferences placing people along a continuum between efficiently seeing people you already know and meeting new people. If you need to get caught up with a number of people in an industry, doing so at an event can save you a great deal of time. If it is an important part of your job to interact with partners or suppliers -- it can be a good idea to batch up those activities at an event.
I submit that unless you make a living on the speaking circuit (promoting your book for example) it would be best to attend events where you meet new people and properly targetted it just might make sense to pay for the privilege.