Speaking as someone who once had multiple LJs to keep fic, other writing, personal life, and religion separate, and friended different people on each: oh hell yes would I have used the combined reading page.

Now that I have pulled all my activities into one identity, my only secondary accounts are for fictional characters, whose reading pages I don't use. But I remember being the use case for the combined reading page. It was the sheer inconvenience of trying to read four separate flists, more than anything else, that got me to consolidate my journaling.