Obviously your choice, but personally I prefer to have different SSIDs for all my WAPs. That way it is immediately obvious which one you are connected to. Devices wil switch between them in exactly the same manner regardless of whether SSIDs are cloned or different.
That isn't something I have ever seen as an advantage in the environments I've been involved with, so have never tried this first hand. Do you find that devices will roam immediately they get a better signal from an adjacent SSID? I would have thought there might be a tendency to hang onto the current association until it actually loses connection before making a new connection. This may be device dependent of course.
Regarding power line adapters, my TP-Link kit made no difference of any sort to ADSL noise margin, speed or error rates. We're on a long line so this may be because our DSL wasn't using the high frequencies anyway.