Chests of all types are almost worthless
I have only ever gotten two SR units. The Comrade Zero from the daily reward. And one Pertinax (now level 20) out of an elite chest. The problem is that past a certain point, rare units and cash are no longer helpful. I have over 800000000 cash that I don't need, and I have at least 20 useless rares of various power in my storage. The elite chests take forever to save up gold for, and they only sometimes give you what you're looking for. I also have no problem training units (I have almost 30 useless trainers). But I can't promote them. I think officer units should be more accessible, and/or chests should be cheaper, and/or cash should be interchangeable for gold.