Thanks you SE for finally understanding inventory issues

[FaileExperiment]

And if you are actively seeking out that mount just think of it as collecting 99 parts of the whistle. Yes, they can take a long time, and yes, they can take up space in your inventory, but "taking a while" is no reason for them to be currencies.
And you only need 1 Mirror or 5 Diamond Dusts per item. Making those a currency would just needlessly bloat the currency menu. You could have easily tossed the Mirror and just gotten another after you finally gotten the globe. you were the one who clogged your inventory with an unused upgrade token.
They are more stamp cards that you trade in. Them being items that you can toss when is much better in the long run than adding new trial currencies every patch.

The reason for them being a currency and going in the currency tab is that they are currency. If you give something to a vendor NPC in exchange for something else and it doesn't have other type of use, that's a currency. The reason it wouldn't have to bloat the currency tab is because if SE programmed it correctly (which they won't or can't do, of course), currency tabs and counters would be dynamically generated only if you have the currency. So if you don't have Horde Totems or mirrors or unidentified arbitrary item #16, it wouldn't have to show "0", instead it'd just not be there.

OR SE, we could just just stop making new currencies and items for every little thing/primal/raid/whatever and stop bloating everyone's inventory.