I'm not a huge fan of the name Igniting as a weapon special ability. Thundering does sort of set the precedence for "On crit, get extra damage" abilities being +1. But the problem with the ability is that it's far more useful against akashic foes, so I don't think that precedence really applies. It makes me wish RGG's fractional enhancement bonuses were a thing in the core rules.
It may be better to have it always do 1d6 fire damage (last I checked, it actually wasn't the most resisted element anymore), and on a crit against akashic foes, it does essence burn and the fire damage is untyped. That may be better for the +2 price, given that you're always going to get some benefit out of it, like the <elemental> burst abilities.
Reverberating is a bit odd too. I like the overall idea of it, but I think it may need to go back to the drawing board, as unlike most other abilities, its value changes with the weapon it is placed on. I'm not so sure that makes it unbalanced per se, but it is a bit weak on the design side of things, at least as far as weapon enhancements go. Is there a way to make it static? On critical hit, 2d6 damage at the beginning of the creature's next turn. +1 enhancement. Just spitballin'.