I think there is some upside from Miller and Jenkins as you describe. The most likely outcome however is that Miller is a 2-2.5 WAR pitcher per year while with us and that Jenkins does not pan out. In that scenario we get a surplus (Miller's output minus his salary) of 5 WAR. The Cardinals get Heyward's surplus this year of about 3 WAR (he is being paid as a 1.5 WAR player and I'm expecting him to be a 4.5 WAR player) plus a surplus of about 1 WAR from Walden over his two years of contractual control, plus the value of a the draft pick which from the various studies I've looked at is worth about 2 WAR. So the Cardinals net 6 and we net 5 WAR. Those are obviously my estimates. Other people will have a different view.
There are two other aspects to this. One is upside and downside relative to the point estimates. I think our end of the deal has more of both because of the longer period we have the players under contractual control. The other is the discount factor. Most of the surplus for the Cards will accrue in 2015. Ours is more spread out over the future, so you want to discount that to some extent.
Bottom line is that this trade is more favorable for the Cardinals.
I like doing this kind of analysis because it takes the emotion out of it. Heyward has been my favorite Brave the past few years. I can see his flaws as a player as well as his strengths. But I liked the way he played and how much he cared. I tried not to let that enter into the assessment above. As I noted, other people could reasonably reach different conclusions about the appropriate valuations of the players involved as well as the draft pick. It isn't a slam dunk for the Cards, but chances are it will work out better for them.
Oh one more thing. If you think there was any significant probability that Heyward would have agreed to a below market deal to stay in Atlanta the trade becomes much worse from our perspective.
If you believe what Bill James has said recently then WAR is not a reliable metric to use at this point in time. Any analysis that leverages this information would seem to be unreliable.