Yeah, I think I'll wait then... until I have some spending money and don't have to give up the really rare stuff.

• The obvious: Watchful score goes much higher. Mandatory for things like increasing SotC if that's what you want to do, and useful for Watchful-scaling checks like The Mechanics Of Progress card.
  
• I consistently get Storm-Threnodies & Bazaar Permits from the 8-action card option. With the goat's Watchful boost, I get a 50ish percent chance and a single second chance gives two tries. Storm-Threnodies are grind-able through other methods, but they're a pain.

• Max Companion BDR without Fate (+2). You can also go to Polythreme to get an Unfinished Hat, mind you, which is easier now that zailing is easier.
  

The Overgoat is one of the few companions that gives you both +Dreaded and +Bizarre. The Overgoat gives them at +1 apiece; the Ubergoat, at +2. This can be immensely useful for lowering your cost of Making Waves, and thus for improving Notability.

Flint has a separate card for each part giving a bonus of four fate total.

As a new owner of an Overgoat, two significant benefits have presented themselves:

• The obvious: Watchful score goes much higher. Mandatory for things like increasing SotC if that's what you want to do, and useful for Watchful-scaling checks like The Mechanics Of Progress card.
  
• I consistently get Storm-Threnodies & Bazaar Permits from the 8-action card option. With the goat's Watchful boost, I get a 50ish percent chance and a single second chance gives two tries. Storm-Threnodies are grind-able through other methods, but they're a pain.

Bonus, which doesn't apply to me (since I own a Bifurcated Owl):

• Max Companion BDR without Fate (+2). You can also go to Polythreme to get an Unfinished Hat, mind you, which is easier now that zailing is easier.
  

Once I get the chance, I'm gonna grind for the Ubergoat so I can 100% the 3-supply Expedition check (plus more SotC). (An Extraordinary Mind or Watchful Destiny owner would probably make do with just an Overgoat.)

One reason I'm very pleased with my Overgoat is that I never sold anything I regretted selling. If anything, I was excessively cautious about that. If you're not sure it's worth liquidating all your possessions to get an Overgoat, then definitely don't do it.

Affair of the Box for Mourning Candles is definitely one of the best grinds. War of Assassins for Collections of Curiosities is even better but as it relies on the Tomb-Colonist card it's only worth keeping a few Collections on hand at any given time. The Fidgeting Writer is best done in large batches to reduce potential losses from variation and also less clicking around in general. There was a thread a month or two ago suggesting using a Gang of Hoodlums and the new Topsy King option of one action for 1 CP casing to go on a heist at the law offices with one Inside Information. According to the post the 5-progress reward is consistently better than the 7-progress reward even if you have enough, as the lower one has the chance of giving a Searing Enigma instead. (Plus heists give some MW as a bonus.) Spirifers can grind Souls through Unfinished Business and trade them in for an EPA slightly above the Affair of the Box, while it's of course difficult to compare to the Fidgeting Writer. With high watchful the Gallery of Serpents is very profitable as with certain choices it gives the (always fate-only) unpredictable treasure alongside Uncanny Incanabula and sometimes bonus supplies. Since they're the same fate cost it's not worth grinding the Temple of Uttermost Wind if you have high enough watchful for the Gallery.

I just bought my first Overgoat today after many months slowly grinding alongside stories and seasonal content. I have the Goat Farmer's Browser Extension installed so can see the total echoes I have available at a given time; since I was getting pretty close already I went through all my items and lowered the number I had reserved of most, so was able to find enough extra cash for the last stretch. Even if an Impossible Theorem is super cool, it's pretty useless and costly to make so there's not much point in having ~50 spare enigmas hanging around.