The semantics and use of the plural marker need more study. I would say that it does not mark just plurality (viz. more than one) but distribution (here and there).
There has definitely been a change since the 1950s. Whereas nonanimates were not (or rarely) pluralized, they are much more frequently, perhaps under the influence of French. Even the demonstrative so 'this' is now pluralized to mean 'these' but perhaps not in all contexts.
Since about the 1970s the plural marker occurs on some or all of the adjectives in a noun phrase. See Samarin (1994).