My thoughts on whether to rope up or not is that that decision always depends on a lot of factors. Some that spring to mind, apart from dizziness, are the potential consequences of a fall, the chance of actually falling, tiredness, experience, and confidence level.
Looking at this photo, I'd say a rope would indeed be overkill for most, but if the lower climber was inexperienced, and the higher climber would be capable of stopping a fall, then the rope could be a good idea, especially a bit higher on this snow slope. I've never been there, but from what I read, there are a lot of accidents on Aconcagua and the fact that many inexperienced people try to climb it plays no small part in that.
Hi Rob, I don't want to judge people, so whatever they feel comfortable with. But, as you mentioned overkill for most.