I have been playing Regrowth effects for as long as I have been playing Magic, going all the way back to... well, Regrowth. I would love to tell you that the first time I cast Regrowth it was to return an Ancestral Recall to my hand, but I am pretty sure it was played to cast two Giant Growths in one turn. (I have since cast Regrowth plenty of times to return an Ancestral Recall, and while dealing 6 extra damage is sweet, it pales compared to drawing six cards.) Anything worth doing in a game of Magic is worth doing twice, and now that holds true for Regrowth as well.
This is exactly the type of card I love to play with, and this version scales perfectly in Commander to suit your progress through a table full of players. I have seen plenty of cards that return more than one card from your graveyard before, but the brand new undaunted mechanic makes this an interesting card to compare to some of the format's staples. Obviously seven mana is a lot to pay for this effect, but unless you are playing some solitaire variant of Commander, this card will not cost you more than six since you should always have at least one opponent. In a three-person game, Seeds of Renewal is comparable to some highly played Commander cards; five mana is the going rate to get back two cards from your graveyard.
Let's take a stroll up the mana curve and compare Seeds of Renewal to some of the cards it will be vying with for space in your green decks.
If you get yourself into a six-player game, Seeds of Renewal is going to crush this card. Same cost but twice the power and you aren't even locked into two mandatory targets, for those situations where you need to play a turn-two Seeds of Renewal for that lonely fetch land (the only card in your graveyard) while stuck on lands. I am not sure I am ready to cut Regrowth just yet—in equal parts for nostalgia and for efficiency. That said, I may very well play both of them.
Seeds of Renewal is rarely going to be able to line up with this card on the basis of converted casting cost, but it does not ask anything else of the cards in hand. If you have ever topdecked Nostalgic Dreams with an empty hand, you know what I mean. My guess is that if you have Nostalgic Dreams in your deck, you have some very good synergy reasons for playing it. It is also much better for green combo decks that want to get cards back and deploy them that same turn.
I don't know how often you get to play six-player games, but for me it does not happen too often. In a five-player game, you are going to pay the same cost for Seeds of Renewal as Recollect, but for twice the output. Even if you think you are playing four-player games where Seeds is going to cost four mana, I am pretty happy to bump Recollect from the roster to make room for Seeds of Renewal. Lots more upside, pretty reasonable casting cost.
There is some value to untapping your lands, especially in mono-green decks where you will untap all your lands and tend to win the clash more often. My guess is that you would prefer to stick with Woodland Guidance in your Kamahl, Fist of Krosa decks, but in my Momir Vig, Simic Visionary deck, I would prefer to have Seeds of Renewal.
Get out of here with your Elven Cache. If you are playing a Rebecca Guay–themed deck, then by all means, stick with the Cache. Otherwise get out of your comfort zone and try something new.
This is the most interesting comparison card for me. The difference is really going to come down to the size of the games you get into. If you regularly play with three or more players, Seeds of Renewal is going to be at least as good as Restock. Yes, it costs more once a player or two has been eliminated but, assuming you killed them, you probably have some cards you won't mind paying a little extra to get back.
All Suns' Dawn
This is a deck-construction question. All Suns' Dawn is going to be slightly better overall in three-color decks and much more powerful in five-color where it can often herald the coming of the end of turns. Even in a three-colored deck, if my play group was large enough I would lean toward the chance to pay three mana for two cards. I can't see myself playing Seeds of Renewal over All Suns' Dawn in a five-color deck, even in six- or seven-player game circles. The payoff is just too high. Although, if I was able to pay one for Seeds, I might just play both.
Casting cost–wise, these are often going to line up well, but the all-you-can-eat buffet of graveyard recursion will let you regrow all your creatures or all your planewalkers or all your sorceries. However, if you wanted to pick up Garruk Wildspeaker and Time Warp, you would have to do so over multiple turns by casting the Renaissance and flashing it back. I prefer the tweezer-like precision of Seeds of Renewal. I have actually been disappointed by Creeping Renaissance in my green decks and generally prefer to have Praetor's Counsel in that slot.
You will notice that I have not listed creatures with recursion abilities like Eternal Witness and Den Protector. I like to have multiple return-from-graveyard effects in my decks and will often jam Witness, Protector, and one or two spells into the same deck. There is zero chance either of those two cards are getting bumped by Seeds of Renewal and a pretty high chance they will all be played together.
Now the question is: what is your nastiest two-card combo that you can return with this card? I know that in Momir Vig I will always be checking my graveyard for Vesuvan Shapeshifter and Brine Elemental (mostly to watch cartoon steam come out of Sheldon Menery's ears). In my Sidisi, Brood Tyrant deck, I will probably just grab Spider Spawning and Gnaw to the Bone for one more play before I flash them back.
What about you?