Arizona's return boils down to this: One year of Martin Prado, six years of a fifth starter in Randall Delgado, two fringy prospects, and one non-prospect. If that sounds like a good deal to you, I have some beachfront property in Phoenix to sell you.
Prado is a versatile player who'll probably be Arizona's full-time third baseman, solving a need for the club in 2013 but at an exorbitant cost, since he's a free agent after the 2013 season. He's an above-average defender at third who generates most of his offensive value with high contact rates; when he hits .300, which he's done three times in the last four seasons, he's potentially a three- to four-win player at third base. (His WAR figures overstate his value somewhat with inflated defensive figures in left field.) He doesn't walk much or have power, nor is that likely to change given his age -- he might creep up closer to 20 homers playing 90 games a year in Chase Field and Coors -- so this is a bet that he'll keep making contact and fill the void at third. That's enough to offset the loss of Upton's bat and glove for one season.
Randall Delgado's ceiling might be as a 4th or 5th starter.
Delgado is a fastball/changeup guy in search of an average breaking ball, without success so far, surviving by changing speeds and by keeping the two-seamer down enough to generate groundballs; if he were to bump up his control by a grade or two, he's got a chance to be league-average in some years, but the lack of an average curveball or slider will make it hard for him to miss enough bats. He reminds me in some ways of Pat Corbin, another changeup guy who's serviceable in the back of the rotation but who looked dynamite out of the pen in brief stints for Arizona in 2012. (You can be very good in a relief role with just two pitches.)
Nick Ahmed was the 9th-best prospect in Atlanta's system, a good defensive shortstop with a plus-plus arm but very little offensive upside; he loads his hands very deep, leading to a long swing, and doesn't have the plate discipline to allow him to compensate.
Zeke Spruill was 7th on my Atlanta rankings, with a low-90s fastball that has some tailing life, keeping the ball down but not enough to make him a true groundball guy; he's got an average slider in the 82-84 mph range and a hard changeup (almost split-like) in the 85-87 range that was very effective against left-handed hitters this year, giving him no platoon split at all in Class AA. He's very slight of build and tends to sling the ball a little from a low 3/4 slot, so I don't know how durable he is. Add in the fact that he doesn't miss a lot of bats with three average pitches and it doesn't bode well for him to be more than a back-end starter.