As far as them offering a better experience, it probably depends on how much you play.  The map, quest, and loot packs definitely improve variety, but if you only expect to play a handful of times, then it may not be worth it to you.  If, on the other hand, you expect to play over and over, then they're (IMO) well worth the cost. As for the Undead DLC, it adds a new and very different faction - I'd suggest playing the base game first and then trying it, as it's probably not a good faction to learn with (and currently not a good faction for the AI).