I think your premise here is incorrect.
It isn't shrinking. It's expanding by leaps and bounds. Why else do you think there's such a rush to buy anything? It isn't folks with large stockpiles; we're already well equipped. It's people who finally realized that they may want to exercise their rights.
I think we're both partly correct. Gun sales are waayy through the roof right now and that's partly due to alot of current gun owners. Look at all the people from these boards who are making early morning runs to walmart to grab whatever they are lucky enough to find. On the other hand there are a lot of new gun owners but how many of them are just buying a handgun or AR because it may be illegal? I'd bet most of the new gun owners won't use them much at all.
So, even though there are lots of new shooters to the sport I think (no research to back it up) that the growth of the gun culture is much less than the overall growth of the population of the country.
We may be winning fights but each fight involves compromise which takes away a bit more of our rights each time. I don't foresee good things in the future for gun owners.