I almost never pre-order (have once ever), and won't be making an exception here either. In principle I like to know what I'm buying first, but with Civ in particular, for both IV and V I found they were not better than their predecessors in their Vanilla versions, and only really hit their strides with the second expansion. So with that background, I'm taking a wait-and-see approach with VI, despite the relatively positive info thus far.
Waiting will also mean there will be community leaderheads to download to replace the super-cartoony ones in VI. I thought the IV ones were bad at the time, but the VI ones are far worse from my preferences. Don't really mind the map graphics since not having too busy of graphics there can be a good thing, but the leader graphics remind me of CivRev more than anything, and that isn't a good thing.