Emanation, not spread. As for the meta, that kind of silliness would definitely be blocked at my table (especially a feat/spell that could mysteriously negate the basic function of an AMF, likewise I don't allow most supplements, they're terrible), and repeating it would get you booted from my group.
Rats, my memory was off. Still, that's a bit worse for the AMF, though, since it also means it doesn't go around corners (fiddling with the base of the cone is thus probably unnecessary as long as you wear sufficiently tall shoes).
I, too, would either disallow that sort of nonsense from happening or warn the player that they're breaking the Gentleman's Agreement and can expect similar horseshit to be used by the antagonists. Depends on the type of game and the players; in the right context that sort of one-upsmanship can generate a pretty fun game, but it's not the sort of thing that works well if one player is trying to force it on everyone else for shits and giggles (even if that player is the DM). So a responsible DM does have to prevent it if it should crop up that way.
Although, many supplements are actually better-balanced than Core because the devs knew what the hell they were doing toward the end. You'll note that the Cone of Anti-Anti-Magic is Core-Only horseshit. There
are valid power reasons for banning them, but they have more to do with the fact that any widening of the field of options makes it likelier that two things will interact in ways the designers never expected to do something stupid than with any inherent awfulness of splatbooks. Still, I've never had to deal with a situation where it was easier to ban a splatbook than an asshole.
The biggest problem with using AMF against wizards is that it's a spell, meaning that non-magic characters actually cannot use it, barring magical scrolls/items. Also, as it is a spell, nothing prevents the wizard from casting it first and using some metamagic to exclude himself from the area-of-effect...
I wouldn't say that's the
biggest problem, but it certainly is one.