Having an Angel’s Mercy attached to a ramp spell isn’t horrible, especially in Limited, and certainly in an environment that rewards Landfall heavily. Were you able to search out any land, obviously, this would be too good. You could just go grab fetchlands. It does feel like 5G is a bit much for a ramp spell. Also, 7 life doesn’t seem like it’s something to care about outside of Limited. However, that is a sizeable amount of life, and can't really be overlooked when considering this card.
In Limited, Nissa’s Renewal is certainly fine. It's more mana ramp than you'll usually see out of one card. At this point on the mana curve, you’ll most certainly have Landfall effects already in play. Paying 6 mana to trigger 3 instances of Landfall could prove quite relevant.
While it's not probably worth casting in most competitive Constructed format, Nissa's Renewal will see play in Commander where ramp is always relevant. In particular, Omnath, Locus of Rage will definitely want this card for triggering its potent Landfall ability of making 5/5 Elemental creature tokens. This is probably a bulk rare for years to come. But if you’re already invested into landfall in Limited, you might not want to find yourself without this card. It's also a good card to hold onto if you play Green in Commander.