Dang it, I was about to post that one! It feels strong but reasonable — I'd argue that Growth Spiral is still
way stronger for the simple reason that ramping on 2 is better than ramping on 3... but that said, I think Joint Explorations is a better card for cube.
One of the nice things about the gold-kicker cards is that they're only
pseudo-gold. While this isn't the case with most of the creatures, I feel like most of the instants and sorceries they've spoiled so far sit in a nice middle-ground where they
encourage splashing for their extra color, but don't
require it. Like, I'd be
reasonably OK with running each of these cards in decks that can't reliably pay their kicker:
EDIT: Looking at some of the older gold-kicker cards, here are some that I'd put on the same list:
Yes, I'm aware that some of those cards don't have kicker. My point still stands.