I'm not sure I agree on the value of the Glyph of Loose Mana. When 6-camping and specifically after having blown cooldowns, the mana gem provides a safety net if you go without an AM proc for awhile. So in a situation where you blow cooldowns, use your AM procs and then have to use 4-5 ABs in a row because of no procs, then the mana gem gets you instantly back up to 100% or close to it. If you do have the glyph, you are still below 80% and still have to weave in some Scorchs to get your mana back up (while your cooldowns may still be running).
If AM procs were more predictable, then the glyph would allow for a more proactive gem use. But that's not the case right now.