For the uninitiated this boils down to any method to gather copious amounts of cash quickly and easily to help you with purchasing upgrades, hats etc.
In Swap Force, it was the sky diamond magic item used while attacking the training dummies---huge payout!
Trap Team was less direct with the Chomp Chest and the buried treasure chests.
I have recently discovered what I think to be the Superchargers version of this. I have not seen it mentioned anywhere else so I thought I would post it up.
It boils down to Legendary Treasure statues placed for display in the courtyards of the Skylander Academy, which is the new hub. (Which I like very much by the way. I DO kinda wish they showed the old version getting pummelled and partially destroyed in the game introduction video but...whachagonnado? The New Yorker coming out in me!)
Anyway, when you put older magic items on the portal, they register and allow you to place a statue of it at the Academy. Things like Sparx the Dragonfly from Spyro's or the Nighmare Express Adventure Piece from Trap Team or the Fiery Forge from Swap Force. After placed, you walk up to the staue and attack it. In short order, it coughs up a useful bit o cash along with some fun animations which vary from piece to piece. Not monumental individually (Monmental for monuments..get it?!?

I'll try to get some numbers on this (If your reading this Wiisdom, I'd love to see it documented somehow).
Happy cash farming portal masters!!