I've added a first run of my spell clarifications to my OD&D House Rules (link under Pages, to the left). They are fairly short, because I'm not trying to tie anyone's hands, just close some potentially bad loopholes.
As for the spells, they are awesome. Even with the (much) smaller lists than later editions, the spells presented are very versatile. A Magic-User is a very useful member of an adventuring party with these spells, and not just as a Flamethower. I can see where Charm and Sleep are much more useful than Magic Missile.
There is a definite lack of direct-damage spells in the lists. There is, however, a wide range of choices which the M-U uses to create a toolbox to help his party deal with unforeseen situations. There used to be a cartoon based on the story Around the World in 80 Days. At the beginning of each episode, the main character would have his side-kick assemble a group of seemingly random things. It would be like "Gather us a table knife, a lump of coal, and a sprig of mint." By the end of the episode he had needed each of the items. That's how I think of OD&D Magic-Users, having to realize what they will need before they need it, and not cornering themselves by limiting their tools. The guy in the cartoon never once said, "Gather us a gun, a bigger gun, a red gun, a blue gun, and a shitpot full of bullets."
The spell descriptions are vague, but rather than focusing on that as a bad thing, I think it makes the spells more versatile and useful. For example, would Move Earth effect an earth elemental? How would Part Water affect a water elemental? Maybe they wouldn't. It depends on the individual referee. The point is, no one's hands are tied. I think it's easier to take the vague wording and put some limiters on it, rather than take a tightly worded spell and tell the players they can do more with it. I think that once we read that tight description, it's how we see it.
I was much more excited about Magic-Users than I have ever been, once I actually read the spell descriptions. It's a fantastic thing.