The ideal strategy is both "tall and wide" by your terms.



Leveling up cities with Burroughs allows for greater Approval in those cities and thus a greater tolerance for more expansion into more regions that have strategic resources and luxeries. Leveled cities get bonus Science and Dust that more than offset the lost Production and Food you might get by using Burroughs to grab as many hexes as possible.



Here is a pic of a leveled city. Check those FIDS and Influence:

Once the marketplace is working fully I'm sure you can use the high dust from a tall empire to trade for resources.



I'm just unsure if the disadvantages of a wide empire are large enough. Each settler you build takes away maybe 1 district. If I have 2 cities and you have 4 are 2 districts and 4 population really gonna help me that much?