You make some great points. I'd love to see things I'll calll "A Dynamic Earth".
Probably for Civ V, rather than a random event proper... It would include things like Ralph's Earthquake zones , and volcanoes.
The volcanoes might start as boiling ocean , or as snowy peaks that first smolder and defrost before they have a chance of errupting with civ III -type graphics. They would be not only be destructive, but create and expand islands, adding fertility to the soil in an area broader than the zone of destruction.
I'd like to see changing sea levels in combination with ice tiles being something like Civ III sea and ocean tiles ( you could cross them, but ending a turn on them would be highly risky) , so that you could bridge the Berring Straits on foot at some point in the game.
I'd like the glaciers to advance and recede, so that there would be fertile fjords in their place and Greenland would be colonizable for a period of time.
I'd like a replication of the "mini-ice age" that brought about the Dark Ages- with land tiles producing one less food. Which prompted your barbarian invasions...
I like your idea about the Sahara. It would be interesting to see it start as plains with several sheep and an elephant or two, with the desert advancing from the west . Another opportunity for barb spawning.