Sorry Craig, I agree with some of the others, who said it's too long.
Mark Twain wrote once, to a friend, "Sorry, I didn't have time to write you a short letter -- so here's a long one instead." It's hard to write short pieces, but the benefit is focus.
I don't agree with those who said CEO's have small attention spans. It's a mistake, methinks, to think this way (because they'll sense one's lack of respect) and the good ones know that by writing something short you concentrate your own attention, and focus. So, first, I'd say it must be short, a page or at most two.
Next, I'd delete the thanks for the party. It sounds obsequious and made me feel, "Yeah, yeah, get to the point." If the party really was that good, and the joke that funny, I'd send him a letter on just that point immediately after the party. He would more likely feel then that your thanks were genuine.
It's not clear to me whether this is a CEO who has bought into ISO 9001, or one that's said "Get me the certificate". Either way, in the introductory paragraph I'd remind him of the context and his involvement so far. If he has not been involved at all, I'd write quite a different letter ... or rather, I'd go visit: you can't build initial commitment in a letter, methinks.
To structure a letter in order to appeal to a CEO I'd try to answer these questions, from his perspective:
What do I want from him? (They often say, "Yes -- but what do you want me to _do_?)
What will be the benefit to the business of so doing?
What will it cost?
Whom else is doing it?
(The letter might not be written so baldly, but these key points would sing out.)
This last question is key, and rarely asked (although Six Sigma programs appear to understand it). CEOs are risk-averse and you can give them all the data and rationale in the world you like -- but if they're the first, or if nobody they know is doing something similarly, and successfully, they'll just hate to be first. Those that are first, the Bransons and Chamers of the world, don't need letters, they're already in your face asking where their management system is.
Just my 2c,
Patrick