Today I revisited Frostflow Lighthouse and Abyss nearly a month and a half (game time) after my previous visit.
The lighthouse had much loot on tables and shelves, in containers, etc. This was probably re-spawned loot, assuming that I took it all during my previous visit.
The abyss had three or four falmers and approximately nine chaurus to kill. However, I found only three glowing mushrooms and no other mushrooms. Many chaurus egg sacs were still empty. Those that were not were concentrated in a couple areas. I recall that I stopped harvesting them earlier due to having become overburdened.
It appears, then, that the chaurus eggs and mushrooms do not respawn in this site even after well over thirty days. What is your experience? In general, I find that some dungeons respawn foes, resources, and loot while others do not. This one looks like a mixed case.