A lot of people will tell you to go, but the big thing you have to think about is your options. If you want to work at a big law firm, it seems that most of those opportunities are doled out during 2L OCI. If you can't make the cut there, you won't be able to land that job (initially).
If you go to a top-20, you're going to be competing against kids who have journals, moot courts and grades. I'm in the top 3rd of my class at a top-20, on a journal (was also selected for a moot court), and I can't even get big firm interviews through our OCI program. I've won legal writing awards, have a great summer job, and loads of extra cirrculars. Not to scare you, but you might not do so hot either.
And for all those who say OCI doesn't matter -- I'm calling you out. It does. I've phoned more than 20 firms in DC over the past few days. I sent them all cover letters and resumes as a "write in" candidate. They told me they only look at write-ins if they don't fill up through OCI. Considering that many visit more than 25 schools, and see more than 18 candidates in a day, I don't think I'll be hearing many positive things about screening interviews.
Your OCI at your current school will treat you much more favorably. If you're personable, and can find a firm you want to work at through your current school, then don't go. Leave for the academic reasons (professor who researches/lectures on an obscure subject matter). Leave for the personal reasons (Grandma is sick; spouse got a new job). Don't leave for the prestige. It's an empty chase.