Potlatch now draws casing (a black outline) for any ways with a highway tag, and fills areas for any "circular" ways (same start and end) with certain tags. The colours need some adjusting: thus far it's only key-sensitive, not value-sensitive, and the casing has shown up that some of the highway colours need to be toned down. But it definitely looks better already.

Note that you still select a way, even a filled area, by clicking on the way. Potlatch purposefully doesn't select it if you click on the fill - because that'd make it pretty much impossible to draw, say, roads within an area with a landuse tag.