sorry for the delay in replying...
The only benefit I see is if it is converted to unicast (point 2), the frame is sent faster and will take less airtime, is that the only benefit?
yes - that's basically it. You can also consider also that in a network of N x APs, that bcast frame will flood out all N x APs, now it's just 1 AP, and unicast at a higher tx rate at that.
If it is not converted, it is sent as a broadcast at a lower speed basic rate, all the stations will hear it, and only the station which is destined for will reply.
also consider the fact that said bcast packet may actually have nothing that will reply, so it's just wasting air time for nothing.