"features that will not improve performance" lol, most of the features don't improve performance
You got culling, so rendering caves isn't a problem anymore. Furthermore without culling, buildings are WAY more expensive to render than caves, because they have way more triangles. Why did you remove caves anyway? The lag spikes were in proximity of a city, not of a cave.
Also I don't see how generating a couple of small caves here and there would impact world generation so dramatically. With all those big cities that need to be generated with lots of buildings anyway.