Well, as a resident of Worcester (Massachusetts) for the last 30 years I can tell you that old-time Mass residents, speaking Boston, pronounce it with no R at all ("Woo -stah"; that's "-oo-" as in "foot") but most people give it one ("Woo-ster"). But then I'm a transplanted New Yorker - from the Bronx, at that - so what do I know.