I can understand your thoughts quite well. Nevertheless it would really improve Kurviger’s functionality and make the two waypoint types much more useful. I think other manufacturers (like Garmin) had similar motivations for implementing such features in their rerouting algorithms.
In my opinion a regular (visit) waypoint should always be default (also if creating roundtrips). Because shaping-points have a somehow less obligatory character so that the user should decide about it.
Sounds like a reasonable solution and helps to keep things as simple as possible. So the existing option “next unvisited waypoint” (for example) would result in a behaviour like my suggested “next unvisited visit-point”, right? I think that would be absolutely sufficient.