Do we need conferences at all?
You don't gain anything by seeing a live talk that you wouldn't on YouTube for instance. It's weird that so many of us work from home but insist on traveling to see a stage show.
"do they offer worthwhile value"
You merely rephrased "need", so I refer to my reply above, same response.Isn't the interpersonal connection and networking from meeting together at a conference what's really important? The added value of a conference isn't so much what is heard from a speaker but the interaction one is afforded while there.
There appear to be enough people disagreeing with you to imply that that is not the full value prop.