In my opinion, Freeman number will always be the prime definition of variety detail but, because it will become increasingly out of date, it will have more and more omissions. Gouby tends to fill these gaps and his identification system is flexible enough to allow endless introductions and his Victorian penny book is the most exhaustive in terms of listing the different varieties which collectors would pursue and label their coins to. Other publications tend to take the difference in varieties to ever more esoteric and trivial (?) levels of detail but which do provide the collector with something to look out for during periods of coin drought.
So, what do people collect ? My theory is that the more money one has to spend on one's collection, the more one concentrates on the "major" varieties, i.e. Freeman and Gouby's original Bronze Penny list (i.e. without the numerous minor date differences etc). The less affluent collector will tend to pursue the esoteric/trivial "varieties" because many of them go unnoticed and can be obtained at less expense. This is my opinion and I may be quite wrong. If I am right, them there won't be much money for the dealer in seeking out these varieties as they won't realise huge prices.
I'm basically a Freeman man myself.