More than 200 Lugh's Cape with extremely niche use, I would consider the idea of getting 2x Bookworm's Cape.
Getting perfect augments on a single Bookworm's Cape is near to impossible, but getting perfect augs for Regen on one and perf augs for Helix on another, is quite realistic!
Basically you could have a toggle.
Regen: Duration (Lugh), Potency (Bookworm)
Helix: Potency (Lugh), Duration (Bookworm)
I dunno, do whatever you like but if I were you I would at least consider the idea.
Going back to your Lugh question.
You can make a pretty generic cape with
INT+30
Macc/Mdmg+20
Mab+10
PDT-10% (or DT-5%, whatever you prefer)
This is not perfect but it's a one-for-all cape that's pretty much good for everything.
Then you could have another one focusing more on Macc for debuffs, something like:
MND+20
Macc+30/mdmg+20
FC+10 (or Enmity-10)
Keep in mind I'm not sure you need an FC specific cape. We have so many options to cap FC in the other slots nowadays... but if you want, you could make a cape like this. Which you would also be able to re-use for heals (enmity-10, MND+20, not too bad if you cap CurePot in the other slots, but then again the influence of MND on C1-4 spells is quite small)
You could also make an idle specific cape focusing only on defensive stats. VIT, Def/eva, Meva, PDT/DT etc.
Then there's specific sets for Occult Acumen, for WS, for Myrkr.
Again... those are extremely niche situations though. For instance on SCH you have the awesome Sublimation and you're not a BLM who casts death and goes out of mana often and needs Myrkr to replenish their MP while locking their MH.
Unless you specifically want to Myrkr or to use a WS for specific fights (and hence locking your MH) on SCH I'd say you can freely swap your weapons ignoring TP, looking for the best idle/precast/midcast options you have available.
I think unless you're someone who considers SCH as his main job, someone who is absolutely in love with the job and wants every single possible niche set, then these options ofter very minimal differences which I'd dare to say might not be exactely optimal for the average SCH player, and more of a waste of inventory space if you ask me.