I’ve found, particularly when there are a large number of players in combat, the names can be a bit overwhelming. I tend to have enemy names on by default, and I find it’s a bit of a sensory overload. Without the names, however, I have difficulty distinguishing friends from foes at short notice.
Perhaps have this as a player option – whether to give full names in WvW (<servername> Invader), or whether to use a more minimalistic coloured dot or icon to identify server allegiance (like what’s been described above), perhaps with a guild tag next to it, so we can still identify which guild an invader belongs to.