1. Contests are loads of fun. Seriously, I can't talk up contests enough. Contests are like an amazing dance party for introverts who never want to leave the house.
She's probably not wearing pants, either.
That's why contests are so important: You make friends, you connect with other writers, you learn about common mistakes, you can find new critique partners, and hopefully you get some feedback (whether from the contest itself or other writers, it's all helpful). So it's worth it to do the contest, even if you're trying to psych yourself out with doubt and lies about why you shouldn't enter. Or just follow the hashtag #NoQS to connect with other writers.
2. I got my agent from a regular query, not a contest.
I know. Crazy, right?
Contests help people find agents. Regular queries help people find agents. Both are totally valid contests. Hundreds of people enter these contests. In the end, it often comes down to personal taste or a misplaced comma (did I mention that you should polish your entries)? So don't think that you HAVE to make a contest or that your life is over if you don't get any requests.
I'll tell you a secret: In my first contest, I was an alternate. Second, nothing. Third, I was picked, but got no requests. It took me until my fourth contest to get to an agent round and receive requests from agents. (I feel like I'm forgetting one. Possibly fifth.) And, still, I didn't sign with either of those agents. But I did meet one of my awesome CPs who has become a very close friend in a few short months.
So: Enter, have fun, be awesome, but don't place too much importance on it. Seriously, if you make a single friend, you win.
(Oh, and did I mention I'm a mentor? Party!)