Hi Eli,
The problem I have with mixing fills, "full" lines and dashes is that it appears like a hierarchical order... Polygons with fills first, then the full lines and finally the dashes. In political maps, dashed are often use as "undefined boundaries".
I have this problem with one of my own maps. I work for a publisher and the designers team always have the last word on the look of everything and they change the symbology of one of my maps because they didn't like it. It was one on Antarctic Claims and as your surely know, some part are claim by 2 or 3 countries. I used dashed lines for all claim boundaries, but where they were 3, my dashes were "overlaped" and they changed it for the map I upload as attachment.
It looks like the Britsh claim is the legitimate one, being in full color and the Chilean and Argentinian are trying to claim a part of Antarctica that isn't theirs. But that wasn't my call in the end. The editor liked it so it will be the one in the book.
Maybe you could try 2 or 3 different type of dashes (like full lines, long dashed and short dashes) and trying to have an equal number of each. No one could think than a third of the boundaries are undefined, but once again, it could lead to other difficulties by overcrowding the map of line symbols. It may worth a try though...
I may not be the best map designer, but I started my cartographic career doing map corrections so I try to stay constructive... If not, do not hesitate to tell me