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It seems like any part that has a lot of flat surface on top will have a really awful top surface, with a rough surface and lots of gaps between the infill, unless I make the skin six to ten layers thick. That burns through a lot of plastic, and I don't remember Slic3r being quite so bad at it. I don't want to print with 33% infill, because that also burns through a lot of plastic. The filament has been measured with a micrometer (six averaged samples) and I've got my extruder steps per mm calibrated as well.

Settings I use are 0.5mm skin thickness, 0.1 layer height, 3 loops, 0.4 extrusion and infill width (with a 0.4 nozzle.) The only thing I can think of is to try a thicker extrusion width. Is there anything else or is this just a drawback of using KISSlicer?

Like you said, low infill ratios leaves a lot of space that the solid layers must flatten. You need to build up the solid layers before you get a smooth surface again.

After seeing some mentions from others, I've found that telling the slicer to use a narrower than normal extrusion width on the top surface gives better results. It's able to get into the smaller nooks and crannies. Slowing your speed to something like 50-60% normal infills will also help.

My top solid surfaces are so smooth they almost look like the bottoms (first layer), except for the glossy shine.