I'm only buying more copies if Soren puts in the beta text-to-speech voices as an option (hint hint). Otherwise, those were some vintage keys I had from a sale that I'd been sitting on for a prime opportunity.
The Real Mars Map Pack is the least valuable DLC, honestly. It's neat to have maps based on real Martian terrain, but I would honestly just rather play on random maps all the time. If you want to throw a bit more money at them, go ahead, but I'd make it the lowest priority piece of DLC out of the whole list (except maybe the map editor if that's not your thing).