Choose R1 and R2 such that it gives a good margin for device variations. 5x will cater to a smaller range of hfe variation than 10x will. That said, where I come from - audio electronics - the goal is not so much as increasing impedance as much as it is reducing distortion and device dependency, increasing linearity, etc - the end goal being a system thats truly "hi-fi" as in which does not add or remove anything from the audio except its amplitude. This is a rather impossible goal given real world devices so we can only try to come as close to a "straight wire with gain"...
And a simple self-biased BJT stage is rarely used for hi-fi. Its usually op-amps...