The Reference List is probably the thing I use least in Scrivener, largely because I keep my references elsewhere.
But when I do use it, it’s important.
What would be very helpful is a change in the reference list icon to show whether there’s something in there or not. (Same could apply to the notes and the keywords icons, I suppose; perhaps outline vs. filled-in. Just something to glance at and think “Aha!”, although to be honest I find myself thinking “Oops” more often than “Aha!” so I could glance at it and think “Oops” but the principle’s the same.)