There's something I noticed when I played the game. It looks like each time Brink uses the crystals, he becomes more "dark", I mean like the colours his coloured with are different. The first time, when we revive him, he's darker than he was before, but when Low cuts his hand, he becomes remarkably "black".
http://www.tentakelvilla.de/dig/screens/dig152.gif)
The characters don't notice, though, or at least they don't say anything about it, and in the cutscenes he looks normal again. I think it can be, somehow, related to the final scene, when he becomes very old, but I'm not sure (we don't know if his new age is because of the crystals themselves or the "resurrection"). Maybe it represents he's beginning to grow old by using the crystals (it's weird Low and Maggie don't say nothing about it, though) and that culminates in his final age at the end of the game.
By the way, there's another thing related to this. When they enter the new ship to go back to the Earth, Brink doesn't look old anymore (his hair is blonde again and all that). I guess that's a minor mistake of the game and Brink is not supposed to be young again, but who knows...
http://www.tentakelvilla.de/dig/screens/dig184.gif)