I think actually when the object gets more complex, it is probably a better idea to do the rebuild method more often rather than try to boolean union new parts on.

With boolean union, there is the risk that you will get additional edges inserted around the new pieces you are trying to attach. The geometry library that MoI uses does some extra work to try and combine planar faces together when you do booleans. This is why your method works well in this case. But sometimes that automatic combining may not work and I don't think it will happen for non-planar surfaces either.

With the reconstruction method you're always guaranteed to get a simple clean result at the end, without extra edges being introduced into the middle of the object.

The reconstruction method is often times faster than you would think, once you get used to the techniques for it. But it takes a while to get comfortable with the techniques though.

- Michael