I'd love for this to be possible too, since I always seem to be short on Sparks of Life and long on Eternal Orbs, but the fact is that OOO benefits financially from having rarities only being available for purchase via energy. With elevators now free, they're the main "everyday" energy sink in the game. Still I wish there was some sort of happy medium that could be worked out, because it's kind of ridiculous to have people sitting on hundreds of Sparks that they'll never use, while others are barely scraping by now that drop rates have been nerfed.

Maybe make them like bound weapons, unable to trade yet you can sell them to vendors at a smaller price than they're really worth.
Although i always support ideas that would encourage team play/helping others.

I'm gonna say no to this one. Unbinding rarities would just bring back alt farming on a whole different level, first off. Not to mention this would damage the rarities market, which OOO makes a bit of precious money off of, as well as some players I've seen finding a way to make it work for them. Even if you just want to be able to help your friends and guildmates out, exploitation has to be considered. Not every player has the moral ability not to take advantage of something that might provide quick money (see the prismatic bolted vee incident).

As far as selling the rarities to an NPC, unless the payout is rather low, its still a little questionable in my opinion, but I have fewer objections to this. just make sure its significantly lower than the actual value of the item, as is the trend with vendors.