Having been to both professional and community conferences I'd say that despite the lack of polish the community conferences are better. There are some good speakers in both conferences, but I find that the professional speakers tend not to show the enthusiasm or passion if that is all they do.
Sure, the professional speaker can put on a good show, that's what draws the crowds. But then again, do I want a good show or do I want to be educated? Bottom line is that I'm there to learn stuff. I can learn much more from someone who is clearly passionate even although they may stumble a bit (because that passion rubs off) than I can from someone who is merely an entertainer.
You may argue that the professional speaker will do a better job. But that's not necessarily the case. I saw a professional speaker, traveled transatlantic to be at the conference, 90 minutes presentation. 60 minutes of waffle about the history of the internet (not the topic), 25 minutes on the history of REST (getting closer), 5 minutes on a REST framework (on target at last), then 2 minutes over time he "discovered" he couldn't show the demo because he had not actually installed the relevant software. I was so angry at that because it was painfully obvious that he did know in advance and instead of giving us the opportunity to go to a different sesssion lied to us all. All the community speakers I've seen at least had the necessary software installed to show off their demos.
Finally, in the interests of openness, I organised a codecamp style event called Developer Day Scotland (AKA DDD-Scotland) the last couple of years. Why? Becuase there are no developer conferences in Scotland for .NET developers. Community conferences fill a niche that the big conferences don't cover.