Here it comes, the typical consultant response "it depends".
Agile conferences can be very beneficial but what it really comes down to is ROI. Does the benefit really outweigh the cost and is there really any way of determining that? Let's come back to that.
The main Agile conference is hosted by the Agile Alliance which occurred last week in Orlando (Agile 2017). There are typically over 2000 attendees.
Scrum Gathering (hosted by the Scrum Alliance) hosts conferences around the world. There turnout isn't as big as the Agile Alliance but that's not necessarily a bad thing.
Finally, the XP conferences are probably the eldest of the Agile conferences. But don't let the XP name fool you. This conference doesn't target XP. It is an Agile conference that brings together practitioners and academics. This conference is always held in Europe.
For first time attendees the value add is around the sessions. Chances are, most sessions will provide a plethora of information. As people become more experienced with Agile, the value add leans toward networking. People may start to form groups and continue those groups via social media long after the conference. In fact, some people attend conferences just for the networking aspect and bypass the sessions altogether.
The 3 conferences mentioned above are more tailored towards ScrumMasters, Product Owners, and Coaches. There isn't a substantial representation from developers. Another important point is that the list is not complete by any means. There are other Agile conferences and there are even technical Agile conferences where many developers attend.
What may be missing is the attendance of C-level executives. These individuals are not practicing Agile and are limited to information of those that closely surround them. By attending these conferences they may be better equipped to ask the right questions and challenge those seek change.
So back to the original question. Is it worth it?
If you come back with 2 or 3 things and actually implement them, chances are it was worth it.