^ ^ They clearly have things they need to do, since they are always showing drones working when they aren't regenerating.
I'm not really getting the part where Borg are vulnerable simply because they're not streamlined. Normally, opponents try to disable them with weapons in the same way as other foes.
The damage enemies can accomplish to the collective through a drone are limited to viruses, which in their deadliest form so far, have not wiped out the collective. The queen will destroy tens of thousands of Borg herself to amputate a malady, so it seems a cost of doing business. And unlike humans, a Borg's memories literally live on as long as there is a collective. Their death has less at stake than for us.