Vector based just casts rays left and right until theres a gap then continues from the gap. I would say it isnt easy for strategy AI and the maps would have to be more simple. The idea can be combined with precomputed paths or navigation points with relaxed (non strict) path following.
About the boundary around the buildings - if you number the nodes from 0-count its easy to calculate the quickest way around the building.
Also, once you have a path with A then you should be able to construct it walking back from the goal. If you make a hybrid with a ray cast then you have to add the path the ray covered to the closed list and do not reset the Astar between raycasts on the same search.
The additional ray cast should link the nodes properly to the searched nodes in the astar search so that the path can be constructed.