I have some thoughts to add. Lockboxes should stick to accessories, but with the tiered key system as described. Shadow keys should be purchased with boss tokens (a suggestion by someone else I saw): this is the perfect way to lock content. You either have to run the bosses and show that you are capable, or you have to purchase them from someone. At the same time, it stealthily burns energy as well, as many people will use CE on their runs. The problem with the current system is that it slaps the player with a huge up-front cost. By spreading the costs into the time needed to obtain boss tokens, you soften the perceived costs, as players are more likely to discount the time they've spent running bosses.

Edit:
Example, assume it costs 50 energy to run a given boss (due to rez, or starting before the terminal) to net 3 tokens
So if it costs 20x of each token, that's about 7 runs of 4 bosses.
7 x 4 x 50 = 1400 energy.
Of course, you could do this on mist over two weeks, and you would get a fair amount of return while running the boss dungeon. But the point is, it takes two weeks, and any time you shave off will cost you CE. The exact token amounts can be modified; 20 is just an example.
This is an example of a gradual cost, rather than an upfront cost. It's exactly why credit card companies allow you to carry a balance. You actually pay more in the end, but you notice less because you're never paying much at any single time.