Is there a case for SLOs?
While this is not a perfect answer (not a rigorous study of the costs and benefits of learning outcomes) I hope it will give some insights. 

Learning outcomes are not all that rare, although I do not remember seeing them much in the US when I was there. 

One of the key reasons for learning outcomes is to be able to evaluate how closely Module A in School X matches to Module B in School Y. If you are teaching a subject titled "Contract and Negligence Law in New Zealand" then the learning outcomes kind of write themselves. If you are teaching a subject titled "Modern Business Practices" then it is less clear what it is that students who passed that subject actually learned.

So, leaning outcomes, I believe, are mainly for the benefit of administrators so that can 'map' modules across universities. However, I also believe that they have great value for us as teachers. I believe the more we can formalize, in writing, what students will learn, the more transparent we are being and the fewer (unhappy) surprises people are likely to have. Students will better understand what they are supposed to learn, as will their parents (if they are involved in the process) and other teachers will be able to see how our modules fit together with their own simply by reviewing the learning outcomes.

Typical learning outcomes might include (in my field): Understanding teamwork and team development. In this case, you do not need to look at differences in test scores. The outcome is not an improvement in knowledge (take a module where you have already learned the outcomes and you will likely learn very little) but rather an absolute "The student will understand this." If the student did not understand before, they should understand at the end, or they should fail.

I do not believe the goal of the learning outcome is that it is one-question on a final exam but rather it is what gets assessed by the assessor. How you do that is up to you. For the example of team work I have several tests to see if students understand the key points that they should have learned.