One thing to (also) think about is:
Many "ancient" resources, flint for example are also the same
basic places where they find shale for oil extraction in the modern era. Flint would carry through all the way to just before the industrial age where shale extraction would begin in the late industrial age. You could control this with A. different improvment methods (meaning eventually you'd work the square twice) with different city-buildings that would become obsolete/become available during the right eras.
otherwise the list looks good. from my own mod I've added:
Hardwood (a reskinned/scaled banana tree) (which looks better than it sounds)
spawning grounds (in ocean/coast) used in different era's for the industrial explotation of different fish. Salmon making the full circle of eras at the beginning and end.
buffalo(american bison) which had major industrial & agricultural use in the early industrial era, after being a food resource from the ancient era
with fruit/grain crops you can control what latitudes resources spawn in the game, with a little tweaking (and much major cussing) you can get rye to grow in the cold climates, and rice in the tropical areas. so you can do multiple (redundant) types without having it be simply a matter of more = better.
Sulphur in the ancient era used in medical/mystical lore, warfare in the gunpowder era, industry in the industrial era.
last note you could do a series of "unique" (flag on resources btw for those who don't know) of resources to create national wonders....mt. rushmore and 3 gorges dam (I know it's a world wonder atm) come to mind, but a "sacred grove", "grand canyon" or "hot springs/gysers" come to mind that woudl give flavor (& sundry benifit)
to me, more is better, more diverse along with more improvements to exploit them, it isn't the most historically accurate thing but it is a lot more fun to look at a map full of 'stuff' than to look at a lot of barren wilderness. just an opinion.
good luck zuul, I'll be looking forward to exploi...er using your work.
