I couldn't find this information anywhere, and I'm pretty sure it's accurate. At any rate, the strategy is working well for me.
So here is how and why I'm doing so good at farming crux. First off, if you don't already know, the ONLY place to get crux is in Northern Craglorn. Keep in mind that shadowhide is also a material that counts and could lead to a crux drop, so some beasts can lead to a crux drop too. All crafting material nodes can drop crux.
Ok, so there is a given drop rate for crux. I think the drop rate for crux is right about 1 crux for every 500 units of materials harvested, give or take 100. I don't know what the exact drop rate is for crux, but let's call it X to keep with basic algebra notation. So, since voidbloom nodes typically drop the most units of the material, usually 5-7 units, then the liklihood of getting a crux at a voidbloom node is 5 to 7 times X. Nightwood is the second best, with an average of 4-6 units of material per node, so the liklihood of getting a crux is 4 to 6 times X at a nightwood node. Voidstone averages 3-4 units per node, so 3-4X at a voidstone node. And finally, enchanting and alchemy nodes average 1-2 units per node, so liklihood of getting a crux at those nodes is the least, at 1-2 times X.
So, the take home message is focus on voidbloom, nightwood, then voidstone, in that order, and you will maximize your crux farming effort. A really fast horse and darting from valuable nodes and ignoring the enchanting and alchemy nodes seems to work best, especially when N. Craglorn is crowded with farmers. (basically, I suggest farming only in off peak times. Combat farming sucks)
And finally, if you have a perk that increases the number of units of material per node that gets dropped, then that should increase your likelihood of a crux dropping proportionally to the perk.
I hope this helps someone. I'd estimate this strategy cuts my time between crux drops by about half compared to harvesting every node.