Basically, your speech lacks visceral impact.
Here is what I recommend: keep your speech as it is, don't edit it in the slightest.
The thing you need to change is the delivery. What you need is some kind of visual aid to keep the audience's attention, it's an aspect of presentation which even some of the most experienced public speakers miss. Now, to add the kind of impact to your presentation that is required for a valedictorian address, you're going to need several dozen brightly coloured handkerchiefs.
Here's how the technique works: Before you perform your speech, get all of the handkerchiefs and tie them together to make as long a rope as you can, attempt to alternate the colours as much as is possible but don't let a pattern emerge. Wedge one end of the rope to the fly of your trousers, then attatch the other end of the rope to your penis, tuck the rest of the lengths into your trousers and let them hang loosely down one of your legs.
About thirty seconds into your speech (when your audience will be starting to get bored), unzip your fly and begin to casually unfurl the handkerchiefs from your trousers, starting with the end that you had wedged into your fly. It's vitally important that you do this motion calmly and without wavering from your speech, the whole point is to make it look like a completely absent minded gesture that you'd do anywhere, even at the Pope's Christening. The trick you're attempting to pull off is to reach the end of the rope just as you finish your speech, so tease the lengths out slowly and take your time with the whole motion. If you time it just right then you'll manage to get your dong to flop out of your trousers just as the audience is rising to its feet to cheer your final word.
Then, to finish the address on a high-note, you should sprint up to the nearest grandmother (probably standing in the front row of the audience) and start slapping her with your wanger. If you really want to get the full effect out of this gesture (and some academics argue that this step is a little more than is strictly required) then you should shout/hysterically-scream "How do you fucking like that bitch? Wait till you see what I'm going to do to your grandaughter, you dirty fucking slut. I'll rip her motherfucking heart out and f*ck her till she screams!"
Trust me, the whole thing will go down a storm, you'll have the audience hanging on your every word and your speech will be easily the most memorable thing that'll happen all day.
Good luck with it!