But an average Googler gets their 20% time, plus a real chance to pitch for more resources. The (relatively flat) management chain is very open to great ideas regardless of where they come from, and willing to invest in them if they're sufficiently good. Mind you that bar isn't met all that often, but it does happen with some regularity.
I wouldn't go to Google for the sole purpose of pursuing your own idea there, but you should feel confident that if you have a great one, you'll be given a chance to make a case for it.
This is from the perspective of a Seattle Google employee, so I don't think location is an issue.