Plausible; but what connection is between green and gold? Or is this just Regrowth but a bit limited so a bit cheaper than it would be nowadays?

It's just a limited style of regrowth (cf. Awe for the Guilds, Pyroconvergence, Ultimate Price, Pure // Simple, Trial // Error, Brace for Impact...), though I should probably consider making it an instant.

ETA: I'd forgotten about Reborn Hope. That card is only uncommon and multicolor due to Alara Reborn's schtick, though. In a ravnica set, the card has significantly less targets.

I think it's fine to be . But I'm not sure about common. I know Raise Dead and Remember the Fallen are common, but Regrowth and Nature's Spiral are both uncommon, as in fact is Call to Mind.