gain of the audio amp depends a lot on the overall gain of the preceding RF and IF stages.... a total audio gain from detector to speaker of somewhere between 20 and 200 is a good ballpark figure
LTspice is good for simulating transistor audio amplifiers, LT opamp circuits and LT power supply IC circuits.
It is also good for simulating anything that you can find an accurate model for.
You will not be able to find accurate models for IF transformers and IF ceramic filters.