I always say that a real writer (someone who expects to be published multiple times over their lifetime) should go to BEA at least once in their writing career.
Most writers think this means that as soon as they have a book to sell they should show up at this mega-publishing event where they have a captive audience of 30,000 agents and editors and hand out 10 lb manuscripts (yes, I have been approached by armed writers), proposals and business cards to pitch their wares.
Writers are the last people editors and agents want to see at BEA. Our focus is on selling rights to published books. We have office hours to hear about new books.
So why would I tell you to go there?
The best time for a writer to go to BEA is after s/he has sold her/his first book (preferably before it is published). When you walk through the aisles and aisles of promotional material for other writers' books that will be published in the coming 6 months, it should give you a really good idea of just how small your book is in the overall scheme of publishing and how hard you are going to have to work to stand out in the crowd.
When you are there, you should take notes on what other books or authors in your category are doing to make their books stand out (signings, costumes, bookmarks, scantily clad men and/or women with fliers) and see if you can be inspired for some unique way to promote your book cheaply (or you can pony up the money). Hopefully, you will be able to meet some more established writers (who are signing) and they will be kind enough to say they will read your book for a blurb. Don't forget to get their email address.
You might also get invited to some industry parties. Here you will schmooze. Do not party (meaning do not drink too much). Make sure you meet every reviewer, journalist and assistant editor in the place and get their cards. Write a thank you note as soon as you get home. Put them on your Christmas card list. This is called networking.
If it was worth while (you'll know this by the contacts you made), you might want to do it again and again. If not, you know what you were missing, whether or not you have the personality to do this particular writer dog and pony show, and just how big and intimidating the wide world of publishing is.
And maybe you'll have a little more respect for your agent and editors who have to do this every year on your behalf.