So perhaps a good "rule" is precision wherever possible, but without compromising aesthetics. Yes, for a fantasy map that does make sense. And, and Redrobes points out, it also depends on the scale of the map. If I'm drawing a city map, I should be precise with a river width. But in a world map, that same river could also be very small or not be there at all. Giving undeciphrable information is not to give information at all, so perhaps some things may be omitted for the sake of clarity.
Also, nice thought, jfrazierjr, with the travel time routes, but I think that would only work with organized routes. Otherwise, one still needs to convert travel time depending on travel method. Still, a map that shows the "standard" routes would be cool.
Lukc (and Redrobes, if he is the author), is there any chance a digital copy of the map could be linked here somewhere? Would love to see it!