I haven't spent any dilithium. I intend to play on the exchange but recently I have only really seen falling prices. When I first started watching, it must have been right about the height of dilithium demand (due to the holiday boxes) since the going rate was about 475/CP. Now that the community is souring to the idea of the boxes, demand for dilithium has decreased. I might try to make a move with my CP and pick some up before the F2P launch, since once that happens, I'm pretty sure dilithium rates will spike.
You have to remember that this "transition period" between the implementation of the dilithium economy and the start of F2P is a bit wonky. The dilithium economy is structured around having a large mass of players in the game who are "poor" on game assets, and have the option of buying CP and converting to dilithium. Right now though, all STO players are "rich" (despite the huge loss we all took on the conversion). Nobody has to fork out dilithium to buy a new ship at rank-up, every player is receiving 400CP/month, every player probably already has a character and a ship that is probably already decently equipped.
The use of dilithium will definitely go up. Either when the F2P members join and need to for buying upgrades, new officers and ships, etc, or the conversion of dilithium to c-points will get so bad that it won't be worth trying to save it for points, and people will just start using it when they need to.
At the moment, people are still used to using energy credits to buy items and don't want to "waste" their dilithium, when it could be going towards buying items in the actual c-store.