I only run doubles, no triples.
Hmm... Come to think of it, I haven't looked into doubling gold cards yet. Maybe there's something I want to double. I'll have a look.
Anyway, as for a motivation.
Champion of the Parish: there's a lot of incidental humans, and Champion of the Parish does a get job at providing your one-drops with reach. If you find the second, you're really starting to pay attention to creature types, which is a fun thing to do in draft every once in a while.
Nyx-Fleece Ram: Abzan is the backbone of my enchantment theme, though blue and red have a few enchantments too, to make the theme viable in other colors. The Ram is my only enchantment creature in white, because it's by far the best fit, considering that constellation is about accumulating advantage over time with triggers. Furthermore it's one of the few playable walls that can actually attack in case of Doran.
Blade Splicer: Both Esper and Grixis have a strong artifact subtheme, but I'm trying to keep it as non-poisonous as possible. White is also the home of aggro, and combines with black for the super sweet (at least that's what I think) attrition archetype abusing the likes of Braids, Cabal Minion and Smokestack. Blade Splicer is a very, very happy intersection of those three very divergent archetypes.
Cloudfin Raptor: without a question the one-drop of choice in blue for me. It attacks well and plays into the Temur +1/+1 counter subtheme (which it shares with Naya).
Gravecrawler: ah, the other creature type I support in my cube. I even run the
Zombie lord, because it's also a decent enough roadblock on its own. Of course Gravecrawler goes into that same attrition based archetype I mentioned before, but it also combines with red in the Grixis "sacrificing minions, what isn't it good for" archetype.
Young Pyromancer: ah, who doesn't love this guy? Great and one of a kind in Izzet spells. A fantastic build-around-me two-of.
Eidolon of Blossoms: a bit of a strange card to double up maybe, but drawing cards is key in the constellation deck, and this is one of the best on-theme ways to do it in Abzan colors. Sometimes it's just a Striped Bear, sometimes it can go nuts.
Bonesplitter: perfect equipment. They won't ever print anything as remotely efficient and aggro-friendly, yet still balanced again, so this is a near mandatory two-of for everyone considering breaking singleton if you ask me.
Cogwork Librarian: won't ever see play (I wish it cost
instead and will probably end up replacing it with two fakes that do just that) but the effect is too sweet to ignore. Worthy inclusions in any cube.
Lands: alpha duals are out, because I think they're too good (virtually no downside at all compared to a basic land), but fetches and shock duals are golden. Recently however I acquired one each of the Khans fetches (finally affordable fetches!), and I dislike playing one proxied and one real fetch, so I'm down to one. I will probably save up to buy a second fetch eventually. Since I run a wedge/shard themed cube triple fixing is important. I run two customs for each supported three-color combination, and two trilands.