No, it doesn't mean that it should just be left. But if someone (one person) notices, and the majority doesn't, that means that Disney is prioritizing their never-ending to-do list. If an attraction is shut down for a refurb, everyone will notice that, and I'd rather that re-openeing the attracting or keeping the AAs oiled and animated take precedent over curtain installation.
Some of the posts in this discussion thread seem to suggest that the Disney Imagineers are utterly unaware of this "visibility problem." Let's think about how many times they had to ride the attraction and check off on every nook and cranny before opening. They obviously know about what guests can and can't see. But what we - the guests - do not know are their reasons for the attraction being in the state that it's in now; what priorities may take precedent over making a dark scene even darker; or what they have planned for potential improvements down the road.