If it's less "I want to upgrade the gear faster" and more just "I hate hitting the nuts cap and having nothing to spend them on", that I can more readily agree with. I tend to think most capped currencies should have some stuff you can spend it on that's a consumable in some form; given a long enough playtime, any currency that doesn't, sooner or later you'll run out of things to buy.
Nuts do offer you materia, as noted, which sort-of qualifies... but the materia is mostly just useful to the people who are doing savage and want to overmeld in week 1. Though even if you don't care about the gil, you mention you'd like stuff you could give to folks in your FC... and I promise you, any raiders in your FC would probably be extremely happy to receive stacks of free materia, especially when 6.4 lands.
But that aside, most other capped currencies (save current tomestones) seem to have some goofy little thing you can spend it on endlessly, like the Icarus feathers from PvP or whatnot. So maybe nuts could stand to have some things like the fancier dyes, little visual things like the Meteor Survivor glamour prisms (that have a meteor crash down and turn into the game's icon) or "Realm Reborn Red" which you shake up and spray like a bottle of champagne, or whatnot.
Unfortunately, I do suspect Deveryn is correct that adding a whole bunch of other stuff (orchestrions, furniture, etc.) to the Nuts vendors is not in the cards; the devs have demonstrably shown that they don't want any one system to be a single way in which you can get all the stuff. Especially since as soon as they do, we as a playerbase have demonstrated we will treat that system as mandatory and flood it.
As it is, hunt trains are already one of the more effective grinding methods because (as you note) you get both types of current endgame tomestone and the nuts, which probably leads to some of the vitriol that happens if a hunt train decides a mark is 'theirs' and then some other group comes along and blithely goes "Cool! A hunt mark! Let's kill that!"
(And if you think people get salty now... I mean, can you imagine the vitriol if in addition nuts were the One True Currency and people felt pressured to grind them specifically?)