Where is the best place to farm sigil powder?
Crafting 90-100 NM dungeons is extremely expensive, you only have a 10% chance of getting a 100 and then it needs reasonable affixes to even try it. Running 90+ dungeons seems to rarely drop new sigils at all.
grandma’s tree 
boring grind
You could just run those 90 ones. There is absolutely no difference in the amount of experience gained or drops.
Ye, I just want the achievement for finishing a 100, have done 96 so it should be doable with not terrible affixes.
the best way is just grind the lower level and then grind the other sigils that drops in it.
Seems like the raw sigil powder got nerfed pretty hard, I used to accumulate a lot passively running NMD. Now I HAVE to salvage sigils en masse to accumulate what seems like anything.
Honestly the game feels significantly worse to play all around right now than it did the first few days on launch.