Implantable therapeutic devices and methods for endovascular placement of devices at a target site, such an opening at a neck of an aneurysm, are disclosed. Selected embodiments of the present technology have closures that at least partially occlude the neck of an aneurysm to stabilize embolic or coagulative treatment of the aneurysm. In one embodiment, for example, an aneurysm closure device comprises a closure structure and a supplemental stabilizer. The closure structure can have a curved portion configured to extend along a first vessel, such as a side branch of a bifurcated vessel that extends along a lateral axis. The supplemental stabilizer extends from the closure structure along a longitudinal axis transverse to the lateral axis of the first vessel. The supplemental stabilizer is configured to exert an outward force against a second vessel, such as a parent vessel, that extends transversely to the first vessel.