That is a good point. Compared to your list I dropped 4 Narcomoeba from my reanimation suite.
They are missed for sure, but the extra cycles are nice as well.
The bigger change was dropping the maindeck blue Forces. I miss those a lot.
Here are the comparisons to consider. The downside is the loss of dredging into Narcomoeba. Lets consider the following scenarios: We will label 4 Naromoebas, 6 Forces and 2 Fields as your "questionable" cards. My questionable cards are 8 Baubles and 4 Street Wraiths.
What if we have 0 in our hand? - In this case you deck is clearly better because you can dredge into Narcomoebas and I cannot.
What if we have 1 in our hand? - If you have a Narcomoeba it is dead. If you have a Force then it is great IF you have a Prized Amalgam. Without a Prized Amalgam the Force is dead too. My extra Bauble means I am likely to dredge 5 extra cards off of an Imp so I start turn 2 with 7 cards in my yard instead of 3. That is a huge difference!
What if we have 2 in our hand? - Now you can pitch one blue card to a Force so this extra counter is fantastic. You can feel much safer. I have 2 extra cyclers so I am likely to start turn 2 with 12 cards in my graveyard rather than 3, which means I am likely to be half way through my deck by the begining of my main phase.
To me by far the biggest weakness of the Baubles is the loss of the blue Forces.
I am not sure about Thug vs Shambling Shell.
In Magic there are some games where you blow your opponent out and there are others where you get blown out. The trick is to win the ones in the middle where it could go either way. Cards that primarily effect that middle are most important. Other cards are "win more" or "lose less." Typically if you have Stinkweed Imp or Grave-Troll pre-board you are doing very well and very likely to win. If you have no dredger at all you are in a lot of trouble. Wasteland will just wreck you. One could argue that 0 dredgers is in the middle, but it is close to you getting blown out.
The important middle section is when you get that Thug or Shambling Shell. Basically if Shell/Thug is your only dredger, then getting 4 chances to dredge into something rather than 3 is a pretty big different and impacts the important games where things can go either way.
Unfortunately there is a very serious downside and it shows up in two ways.
First is your opponent goes turn 1 Oath and you have no green spell to pitch to Force of Vigor.
The second is you do have a green card to pitch, but said green card is Golgari Grave-Troll. I would MUCH rather pitch a Shell so I can dredge my Grave-Troll rather than pitch my Grave-Troll so I can dredge a Thug.
There are also games where I end up with 2 Thugs in my hand. Since I run 4 of them this is actually reasonably likely after a Bazaar activation. For this reason I think running 4 Thugs and 0 Shells is the wrong ratio. I think at least 1 Shell is worth it, maybe 2.