Depends what's changing about it. Sometimes I'd say the evolution of media points to genuine improvement, especially when you see it in relatively new branches like rock and roll or comic books or film; we've been doing some literary forms for a very long time. Often, though, it reflects external changes in technology or education, changes in language, or just differing tastes and preoccupations. And even that might be assigning too much rationale: sometimes it's just a random walk based on recombinations of whatever's been popular in the last thirty years or so.

With this in mind, I'd say modern writers are likely to get more out of responding to technological and social changes than trying to improve basic technique. Reading techno-thrillers or near-future SF, for example, is vastly different when you've got a Wikipedia tab open, and yet I can only think of a couple of writers that seem to have realized this potential.