How common are these hungry nodes? I have yet to see one.
In terms of a fully zoomed map, which is 2048x2048 blocks (1km from center to edge) there are 16384 chunks in total.
The default node rarity will create 1 node in 36 chunks, so 421 total nodes.
1 in 18 nodes will be special. 24 nodes in that entire area will be special.
Nodes can be normal, sinister, unstable, hungry, but also have strength qualifiers: dark, fading, (normal) bright. Which makes a number of valid combinations. So its unclear, out of the 24 nodes, how many would (statistically) be hungry. But its probably close to 1.
Many nodes spawn underground or over bodies of water and might remain undiscovered. This maths also means that ~50% of all 4km square areas have 1 hungry node, 25% will have none, and 25% will have 2 (or more) so theres no guarantee theres even 1 to find.
Pretty rare all things considered. I havn't ever found one either.