've really soured on Crucible. Being colourless gives it this allure of being playable anywhere but in practice even decks that should want it rarely do.
The colorless on Crucible doesn't do much for me either because I've yet to see a non-Green deck use it super well.
So I've been combing through drafts of my cube and Erik's to find decks that use Crucible to prove you wrong and to my dismay, I've learned something. Turns out, you are both right. Not very many decks use it and those that do, are 95% (made up number) Green.
I was under the (wrong) impression that self-mill decks would be using it as a value engine, but that's apparently too narrow. The self-contained engine of LftL is much better for those decks.
I am still considering the Crucible for my MP cube because it is less vulnerable than the Excavator and it has the explosive potential with Fastbond. But thanks for the reality check!