The menu on the conversations list offers four options: Settings, Mark All as Read, Tell your Friends, and What's New. It would be nice to add an option for "Unread only" to show only those conversations with unread messages.

When this option is selected, only conversations with unread messages (those spam messages you haven't deleted yet, the texts you forgot to deal with, etc.) would be shown.

Perhaps at the top, where it says "Textra", it could change to "Textra - Unread Only" (and maybe even, it it's possible, tapping that would switch back to all conversations. Otherwise, from the menu.)