Some OG tunnels feedback after xping in there a bit (was told to post here):
1.)The platinum drop rate is pretty bad. I don't have an exact plat/hr number, but it feels much worse than the other top xp zones for the difficulty of the monsters.
2.) It would be a really neat mechanic if rust spawning the named was something that could happen down here. Each named (Watcher Fenrik, Guardian Sela, and Caretaker Keria) could be spawned randomly by killing "an infested watcher", "an infested guardian", "an infested caretaker". I think this would help people xp down here a bit more instead of just sitting on named spawns every 45minutes.
3.) The main draw to tunnels used to be the opus drops which obviously don't drop anymore. Adding WI/ED/lustrous stones to their loot table would help in giving a reason to grind.
4.) Adding some sort of teleportation hail from the hallway before jenrok up to the ramp leading down the Monstrosity would help this area have a "loop" to grind without having to evac to the entrance every time you wanted to restart. Perhaps this isn't a big deal and could be exploited, who knows, but running back from the zone ent through all the plants/oversized plants/mushroom traps was unenjoyable.
I think my favorite idea is #2, as the Jenrok item quest is still gated behind a 7-day spawn in Jenrok, I don't think increasing the frequency of the named down there does anything to the balance of the game, especially with new tiers coming out and these items becoming mostly vanity items.