Yes, on update the structure will be traversed up, so the parents will be updated. For each change, you'll have as many updates as there are levels of inclusion.
But I'm not sure how big this problem is. I'd say it depends on the number of levels you hierarchy has, and the number of fields a node has indexed. But you can easily abuse both
I'll tweak the code a bit so that it tries to optimize the upward update. Basically when checking a node's root aggregate, if this is already on the update list, stop there, as all its parents are already included in this update.
I agree on having a soft rule in place for recursive aggregates (lets say max 5 levels deep), but I think having a recursive=true rule doesn't help the average copy-paste-from-the-wiki user
(and by the way that includes me too, as the docs are not excellent