Actually AGC design is one of the most important part for good overall receiver performance. This is most seen in HF communications receivers that have to deal with large signal level variations. The well designed AGC system should be able to allow the receiver to work over it's whole dynamic range. The AGC also has to be able to deal with the different modulation modes that it is designed to handle (CW, SSB, AM, etc) as these require different attack and decay time constants. Also each mode have different IF bandwidths requirements and bandwidth filters are usually the most expensive stages in a well designed communications receiver. I've seen some advance AGC designs that would work well over a 100+ DB range.
I would suggest checking out some of the more advanced HAM radio sites for examples and suggestions. The good news it that there are very good devices available for RF, mixer and IF amplifiers these days.
However the current state of the art design in high performance receivers are so called 'software controller receivers', where the AGC, demodulation and bandwidth control are all done using DSP techniques.
Lefty