I think that Class 3 will no longer show the kind of appreciation that it did in the 90s... the prices are already outrageous and beyond most buyers. As the prices rise further, the market will shrink.
"Assault Weapons" on the other hand are relatively cheap to buy now, and as the posted says they would appreciate a lot if another AWB like the 1994 Crime Bill passed. Of course, this would be a gamble, as such a Federal ban would more likely look like the current CA law - no transfers/sales, even by inheritance.
Guns are a risky investment due to the vaguaries of Federal legislation. For my part, I am buying for my own collection unless/until a new ban becomes clear, at which time it may make sense to buy for investment purposes. Even then, it would be a throw of the dice.