Great question - if you are spending the time and money, might as well make it super useful! Love the emphasis you did on "meaningful" - to me that is only achieved if you "rapid fail" a number of interactions that are not, so you have a chance to get to people who are the ones you can engage with. This can be best accomplished by creating a large enough volume of interactions and then pursuing the most useful ones:
1. As soon as you are thinking of going, post on LinkedIn and Twitter (and maybe Facebook depending on whether you are using it work-related or not) - say you are thinking of going and ask if anyone else is. Several days later, post again and ask has anyone been in past years, and what did they think. Then post again, to tell folks you are signed up to go. Don't worry, this is not spamming - as most people miss most posts, you will be lucky to have a few replies.
2. Also check Reddit and Quora - similar approach - esp if you are in Tech.
3. Before attending, use the Twitter hashtag and share your excitement to attend, questions you would have for given topics or speakers and add their @name - many actually reply! Make yourself a Twitter list for the event.
4. At the conference, continue to engage on Twitter. If they have a conference app such as Bizzabo, register and see who else is at the event.
5. "Speed date" networking: When waiting in line at the lunch or sitting down with strangers, ask not about the weather, but state something new you have learned at the conference, and ask them what is their take away. If nothing meaningful, wish them a great conference and move on till you find someone who gives you an interesting answer - then engage.
6. Sometimes I use clothing/bag to engage - as I am a Canadian - a logo from my home town and country usually gets folks to approach me and start a conversation (one of which by the way led to an impromptu memorable chat with Biz Stone). A T-shirt from a given tech tool /company I use also gets like-minded people to reach out.
7. Last but not least, at the event, smile and have fun, and go for what you feel like doing. One of my best work connections was made when I skipped a session at the SalesForce Conference in SF and instead played in the conference provided giant chess in the sun outside. Things happen in mysterious ways, so follow the force!
And congrats for being selected for the WWDC14... I hear it's not a given. ;)