I believe it may be worth saving Motes of Enchantment, the lootbox currency that comes from a couple other things in the game, for level 100 when we get imbue Legendary Items. However, things might change with this, depending on what the 2020 LI Revamp brings!
For anyone that doesn't know, imbued LIs are extreme consumers of Star-lit Crystals and Scrolls of Empowerment (Anfalas versions). Star-lit are very important in upgrading the "stats" of an LI - DPS/healing/whatever main property your item has. Scrolls of empowerment function similarly, allowing your legacies to continue to be leveled and become stronger. The imbued LI system begins at level 100 and your imbued LIs will be ones that scale with you throughout the rest of the game (with the help of star-lit and empowerment).
At the Motes of Enchantment vendor, I found a mega Star-lit Crystal and Scroll of Empowerment. This appear to function as a catch up mechanic, allowing you to quickly upgrade your stats and legacies to 58 and 74, respectively! I checked my characters on Arkenstone, it looks like this would be quite the significant boost to us at level 100. The whole imbued LI grind was already a lot when they were introduced and kept getting more and more through level 120, but it looks like this will make the grind take a lot less!
Here is a screenshot of the vendor with what I am talking about:
This won't really affect us for a few updates, so things could change. I thought it would be good to get the heads up, though, in case it may help anyone. In the current state, it will be worth saving a lot of Motes as someone with a lot of alts that I would like to get respectable LIs on.