To be honest, I am not 100% sure that using the rear heater wires as an aerial is the best technical solution, but I can understand it avoids spoiling the lines of a car with unsighly floppy things.

Mine is not too bad, as long as I am not too far away from the station, definitly not as good as a home getto blaster or something like that.

It may be worth changing the booster as you said, but, I would first make sure you are actually getting 12V to it, there is a wire from the head unit which tells it to power itself on. Could save you a few quid.

I changed mine a while ago, I remember it being a pig of a job though.