The Repair Rune Pouch spell has no effect on the massive pouch. When it reaches its limit of usage, it will crumble to dust with the message "Your massive pouch crumbles to dust as you empty it." It will happen on the 44th time you empty it. Therefore this means each massive pouch can hold a maximum of 756 pure essence. At level 90+ Runecrafting you can get upwards of 2600 Runespan points an hour which in turn can increase experience an hour at the Abyss.