I have an odd confession to make: I'm not quite sure what to spend my gold on. I don't currently collect anything in particular. Buying gear for alts seems somewhat counterproductive, since one typically outlevels gear before using it more than a day or three. I don't aspire to any mounts I don't already own. Bags, maybe? I'm not really sure what I should be spending all this gold on, so it just sort of piles up.
That's not to say that I hoard my gold, though. I piddle it away it little dribbles: 500 gold to an alt here, 500 to my daughter there ... It's enough to prevent myself from developing a dragon's cache.
All around me, though, I see players busily padding their caches for good reason. They're saving for rare pets, special mounts, unusual pieces for a transmog set, or any number of long-term goals. Every time I set a similar goal, I lap myself; another expansion or content patch comes along, and the goalposts move before I'm anywhere close to purchasing my heart's desire. I end up shrugging: "Huh. Well, then ... Bags?" And away goes another set of care packages to my alts.
What are you currently saving your gold to buy?