Really good question and to be honest I do not know. I thought that e.g. a weighting with foot which is much less hierarchical than with car will always give more visited nodes but (from a few examples) I think this is not true.
Following things are important:
1. get getMinWeight right not too high and not too low as either performance is not optimal or correctness.
2. reduce the number of possible ways as much as possible and move all calculation out of the Weighting in a preprocessing (of course, this does not affect the number of nodes)
3. the more landmarks the better
4. maybe you try manually picked landmarks (prefer those at the border of your area). But highly likely our automatic detection algorithm is already very good here.
5. Try changing the active landmarks, although here the defaults should be good already