As I'm sure has been said 1,000 times. . . there's nothing to spend them on! It's silly that everyone has so many. Please just give us stuff to throw them at. Here are a few examples, or suggestions, humbly:
a formal tuxedo; airplane; Wallpapers; mobile wallpapers; "movie quotes" lesson; super week double or nothing; Ad reduction? Bonus heart for test out (like used to be); The Quiz (with answer review);
It is still fun and rewarding to earn lingots, but with nothing to spend them on, they lose their appeal. Maybe make an option where the group admin can require participants to buy in for 5 lingots and the pool will pay out the top three? Just some friendly thoughts.
There have been many "competitions" where the host asked competitors to donate 5 lingots for a chance to win all the donated lingots if they get the most XP during the competition. The host collects the lingots and never pays out the prize. This has happened so often that staff have asked moderators to treat ALL lingot posts - asking for, giving away, competitions that require a donation, etc. - as regular spam posts. More info about that can be found here: https://www.duolingo.com/comment/22343370
I would post a new thread on ways to proper use the excess of lingots we have and ask for suggestions, but the way these forums work the thread would be buried and forgotten in 2 or 3 days... no matter how many upvotes and comments it had... and then a week later another similar thread would come along and this would be a viscous circle. On top of that, nobody in power would read anything.
Lingots are nice at the start... you have few and some things to buy at the shop, but as you progress your course and earn more they soon become irrelevant.
Anyway, here's an upvote to your thread.
It might be good for more things to be added to the lingot shop, but I think eventually having more lingots than can be spent will happen with any reasonable shop, except something like increasing the cost of the streak freeze by a high percentage of the user's current total lingots. In the end, I think it's not very important because it doesn't seem to affect learning very much.
Maybe add more but put a limit on it
The post above this one might deal with a level increase. They both kind of tie though. At some point you learn every thing you can from this and need to find other resources to continue learning. There needs to be end: with levels and with buyable items.
Ever play Cake Mania? The games allows everything to be upgraded but only to a certain point, then the money earned is pointless. Now that usually happens towards the end of the game.
It would be nice if they had enough stuff to spend lingots on, but maybe just enough things where you could have bought everything if you completed the tree.