Seems like a logical move in a lot of ways. It's 126 miles between Memphis and Greenwood, which is the longest gap between stations on the CONO route. Furthermore, under its current schedule, the stop will occur at a relatively reasonable time of day (roughly 8 a.m. southbound and roughly 9 p.m. northbound).
That said, I think they'll be sorely disappointed if they're relying on inbound tourism to make this stop successful. From a logistical standpoint, what exactly are "Blues Trail" tourists going to do once they disembark in little ol' Marks? Walk over to the Hertz counter? Not exactly. Admittedly, I've never been to Marks but the Google Streetview images suggest a town that's neither quaint nor bustling. So they'll have to figure that part out.
But in the sense that it will serve area residents who wish to travel to Chicago, New Orleans, etc, it seems like a good option.