The only type of anime of XIII I'd be interested in would be a Devil May Cry anime type thing. Basically, it would serve to show what the characters are like when the world isn't about to end and they are hauling ass to save it . Maybe we'd finally find out some personal details about Lightning. What does she do for fun? Does she have hobbies? What is she like when with [insert character here]? You know... the little things that help you connect with a character. Or maybe the could actually have interaction between Lightning and Vanille; Snow and Vanille; Hope and Fang; etc. since, you know... they refer to each other as family yet we never really saw them interact with each other.
Otherwise, no. We don't need a retelling of XIII in anime form. I mean, don't get me wrong, I do like several anime series like Trigun, Spice and Wolf, Hellsing Ultimate, Cowboy Beebop, Claymore, Black Lagoon and several others. But there is nothing to gain from watching XIII in anime format as the XIII writers have already proven that without the use of the Ultimania, Novellas, and the Datalog/Fragments they are completely unable to handle exposition, world building, etc. At least with video games they can add in the Datalog/Fragments on top of having a dozen hours of cutscenes.
Currently going "squa squa squa!" To the Devil May Cry franchise: http://25.media.tumblr.com/tumblr_ls0e5g1oWn1qjkv09o1_500.gif... at least for now.