I'm hoping they don't overdo it on the map packs. Some can be OK, but they're basically a poor man's scenario. Ideally, I'd want one or two Civs or a noticeable addition to the core gameplay. I'll settle for a professional scenario combined with a Civ (and probably featured in it).
Basically, if they include the Inca and Maya, plus a map of Mesoamerica, I'd pay $5. If they included Inca, Maya, and a Mesoamerican scenario (with some kind of actual gameplay changes to go with the Civs being placed in their historic settings), I'd pay $10. If they added the Mongols and maybe a gameplay mode where you can play as Barbarians, I'd pay $10. If they added espionage, units and improvements necessary to make the mechanic work, and perhaps a Cold War scenario, I'd pay $10.
In other words, the possibilities are endless, but they have to be willing to give value.