If the design of the system is good, the overhead of stocking is going to be cheap. I mean, communications to the box says "put these discs in these locations", the guy opens the box pulls out that "tray" or whatever (many possibilities here) and replaces it with another that's also been computer and roboticly stocked, you're done.

Maintenance is a bigger unknown to me, but seeing as how they're in their 3rd? generation, they seem to have that under control. Capex could be the big one, those machines and their DVDs aren't cheap ... but they've been keeping this game going for quite a few years. A serious analysis of their financials would be required to make a guess of that, assuming their public owner breaks them out sufficiently.

Ah, and that company does the Coinstar coin cashing kiosks, so that might improve their servicing situation.