Question of the day: Would you consider the fiction equivalent to platform building akin to attending conferences or networking in genre specific group, for instance RWA, or entering writing contests, short story, first chapter, etc? In those instances, do you have to walk a fine line between the value and exposure of those experiences against allowing those venues to keep you from finishing the novel, or the query, to ultimately get you published?
Building a platform, whether in the fiction or non-fiction arena, is all about name-recognition, something that will set you apart from the thousands of others who do exactly what you do - i.e., write a decent-good book on a specific subject or in a specific genre - and that will give a publisher reason to choose you over the thousands of others. As far as fiction goes, as I mentioned before, having a strong platform isn't as necessary as in non-fiction: the average debut novelist probably isn't a household name, but if you are one, or if your name is at least recognizable in some circles, certainly, this will help your cause.
I'm sure that being a member of RWA and the like will help you network, which will undoubtedly help your career (and as I noted last week, having writer friends is invaluable), but I'm not sure that this is part of a "platform" in the truest definition of the word. Landing your short stories in notable journals or winning/placing in contests is...sort of. What these credits really mean is not so much that you'll sell more books because people know your name but that you're a better writer than most aspiring writers, and chances are, you'll be taken more seriously from the query letter on up.
If you're serious about pursuing your fiction - and most of you are - I do think the best thing you can do is write the best possible book and not worry about the rest. Enter contests and land short stories if they fit into your game plan, but as you noted in your question, they can distract from your ultimate goal, which write an incredible book and then sell it. There are enough landmines to worry about in this industry - don't complicate it if you don't have to. (Non-fiction is an entirely different ballgame. Then you can sweat it because yeah, you have to.)
But what say you readers? If you're aiming to be a published fiction writer, have you built your platform? If so, how? And if not, why?
(P.S. - I hope this post is coherent. I'm unthinkably exhausted from the weekend, and I'm not sure if I'm making sense!)