anallawalla, is it possible to use mirodata for City Name and zip only? Which Syntax do you recommend, as I find the guidance in GWT a Little confusing (at least for me). Thanks for sharing your insights and experiences (effect on SEO?).
Also, with regard to organic search by location, I think you'll find that zip codes are scarcely used by searchers at all. You'd be much better off targeting by placename. See discussion in this thread, which most probably will differ in some details from what you'll be doing, but the placename vs zipcode considerations will be the same...
Whether you'll need individual placename landing pages will depend on how competitive your target terms are in the given locations. In my experience, it's getting much more difficult to target multiple locations on one page.
Multiple landing pages, though, are likely to require content that's sufficiently unique for each location. Optimizing for a service area business is also more difficult than optimizing for separate physical locations (which would each have a unique address).