My husband and I are grads and are going through the MALO training right now. Our son just went through the process and was frustrated since there aren't any MALO's in our area. From my understanding, there are far fewer than there are BGO/ALO's for the other branches, and especially if you go to SLS, most likely your interview with your SL there will count as your MALO interview. My son went to SLS, interviewed there, but then never completed his WP application (he has appointments for Navy and AF). We're hoping to keep this from happening with other candidates since he was never able to find a MALO in our area at all.
From what I've heard though on these boards and from others, MALO isn't really make or break. Maybe just break!
If the MALO likes you and lists you as number one on his interviews, etc., that may help you slightly, but certainly won't get you in, no matter how much they want you to be. If they strongly DON'T like you though, yes, it could probably keep you from getting in. And of course I don't mean just personality - if for whatever reason they don't believe you'll be a good fit (doing it for someone else, poor academics, arrogant attitude), then yes, a negative ranking could hurt you. I think in general most liaison officers for all services are there to HELP you as the candidate. They're your information source, your cheerleader, your helper. So unless you really give them a reason to NOT support you, they will. And the academies expect that. So your MALO saying you're the best thing since sliced bread - well, they expect that. But your MALO saying they CAN'T endorse you - well, there'd have to be a strong reason and it WOULD be noticed.
Going back to the introduction question - yes, I'd definitely email and introduce yourself. However, keep in mind that all liaison's are primarily concerned with 2014 right now. Getting in the last interviews, answering questions, helping candidates with nom interviews, etc. So they'll probably be glad to answer some questions or emails, but not to have a long detailed meeting with you right now! Come April or so, when 2014 is settled, you'll start to come up on the radar. WP's application window didn't open last year until in August (for anything other than SLS). My son had his entire Navy and AF applications complete (and an LOA from Navy already) before he even had a chance to apply for WP. But keep in mind that people DO get LOA's based off their summer seminar info. Keep it as complete as possible and do well while there. And don't waste the summer - before school gets out, get letters of recommendation from anyone who you'll want them from. Get phone numbers and emails from teachers who will have to fill out your teacher recommendations (Math/LA/Science) so you don't have to wait until school is back in. Start Dodmerb as soon as you're contacted. Get your MALO interview (if applicable) as soon as you can.
Good luck!