I know what you mean about Sol Rings, I have 2 pages of them in my trade binder plus one in almost every deck, and some that are sitting in a binder of EDH staples.
I originally started out trying to complete the Chromatic Challenge, but now that I'm halfway through and don't play more than half the decks I really don't see the need to finish it. If anything I have cards spread out among decks that would make the ones I do have better. (I too try to not duplicate cards across decks unless it's common cards or lands)