in the case of series resistor, the input voltage available for LM317 will change as per the load current.
Yes it will vary as the load current changes, but will not be a problem as long as the current drawn is <=0.6Amp
In view of power economy, i feel the switch based solutions are efficient and perhaps may not be so costly. with an additional 5 or 6 components the job is done.
With regard to efficiency I agree!
Datasheet of MC34063 attached.pehaps there are cheaper Switches available off late.
as the power requirement is more than the capacity of this IC , an additional pass transistor may be required.