Since I'm level 32 now, I can upgrade to augmented chain armor. If you follow the link to wowhead, you can see that these are level 37 items. Which should mean that an enchantment like Enchant Bracer - Assault should be usable on them, because the enchantment "Requires a level 35 or higher item."
Except that it doesn't work. Attempting to use a scroll, at least, results in an error message that tells me "Target is too low level."
Some comments I've come across online seem to indicate that in some cases "Requires a level X or higher item" actually means "Requires an item that you have to be level X to equip." If that's the case here, I'm going to have to stick with lower-level enchants for the next 13 levels or so.
Addendum: on the plus side of things... after gearing her up in the augmented chain armor, I really like the way it looks. There's a definite "space marine" vibe going on there.