I think the answer depends a great deal on the nature of what you’re writing (and perhaps the degree to which you’re really a hermit). It is almost impossible to promote nonfiction without having the author engage with the world in some way. You can probably get away with avoiding public-speaking events, but if you’re not willing to, say, do an NPR interview about your book, that’s a problem.

Fiction is a little bit different. Whether it’s intended to be high literature or complete pulp, it’s all about what’s on the page and how the reader responds to it. Yes, an author who is willing to do anything and everything to promote his book is valuable to a publisher—but that book has to be good. All else being equal, having written identical books, a social butterfly is more appealing to a publisher than a hermit. But they’d never write identical books, of course! And, speaking for myself here, I think the best fiction requires a kind of monastic discipline, even obsession, on the part of people who create it that doesn’t necessarily lend itself to a raging social life, or building a “platform.” So just be you, and focus on making your book the best it can be. We spend enough time broadcasting ourselves to the ends of the earth, and to me books represent a respite from that. Literature needs more hermits, I say!