Q: Can I use A Good Harvest (AtS 10) to play a 0 cost card without a resource match?
A: No. A Good Harvest only allows you to spend resources for the named sphere, a resource match is still needed to play cards with no resource cost.
Now that we have that important bit out of the way, let me just say that A Good Harvest is amazing! It allows you to do 2 things: 1) play off sphere cards (e.g. put Steward of Gondor on a hero using any resources in play) and 2) smooth resources in multi-sphere decks (e.g. spend excess resources to pay for your hand full of cards)
Tri-sphere decks everywhere got a lot more interesting when this card was released.
A Good Harvest is not just good, it's great!