The Torc is just one of many rewards that we either squandered or never made good use of. I guess it's unique because we didn't vote for it, but still.
I wouldn't say squandered, more like it just didn't fit with how we wanted to act as Mathilde. We did one "charge at the front lines" fight at the East Gate and then joined Clan Angrund in the anticlimactic fight in the Cavern of Stars, but otherwise we acted as an assassin, saboteur, scout, and on one occasion a general, but we didn't lean into the "knight on the front lines" role when given sneakier options.
And thus the torc never really saw use, because the two times we might have made use of it we had no need of it--leadership buffs weren't necessary for dwarves charging to reclaim their ancient home, especially against already broken goblins fighting each other.
So we gave it to the Undumgi to serve as a badge of office for their leader, which seems like a worthy use indeed, and one that will last.
By contrast, even though we have yet to use our Hysh-enchanted poison/disease cleansing item, the purpose of that item is to serve as a very important save against specific and uncommon but deadly threats to Mathilde specifically (but potentially allies as well). It's the kind of item that you're very glad to have when you need it because chances are good that you'd be in deep trouble if you didn't have it--and while we're not fighting Clan Eshin or Skryre anymore, the druchii probably use poisons sometimes and the possibility of running into Nurgle forces can't be dismissed.
I really wish the Battle Mammoth Altar was more popular. It's a good mix of indulgent prestige project and following up on IC regrets that would push us towards at least one large scale battle to test it, without needing us to constantly use it to justify its existence.
The problem with a Battle Mammoth Altar is that it's a combination of high-maintenance (needs to be cared for, fed, entertained enough) and limited duration (a single mammoth has a limited lifespan and mammoths are not a repleneshable resource for the Empire), on top of being something you keep in your strategic reserve for major battles rather than a tool you potentially use in every fight you get into (like the armor of von Tarnus).
In that regard, the magical airship at least has the benefit of not having a lifespan and being very mobile, so it's a lot easier to bring to bear and can carry its own supplies onboard, unlike a mammoth that will need to either be given food where it goes or require you to bring a lot of food with you when you travel with it. Plus, the magical airship has uses outside of combat, unlike a walking Battle Altar.
Remember, we are not a Battle Mage. We might dabble in building or commissioning magical superweapons, but we very rarely go looking for a big fight to actually
use them in, and almost as rarely find a big fight seeking
us.
In terms of IC regrets, not taking on an entire tribe in their own territory without killing their mammoth and somehow taming it, while justifying taking it with us to the expedition that had won bloodless free passage and wanted to just get home...yeah, that's more of a passing fancy. A real IC regret would be more like not going all the way to Karag Dum and solving that mystery, or Gotrek's horribly unlucky death.