As an L.A. native and museum/history afficianado, I have to ask...

Why in the world do you want to visit Olvera St.?

It's a bad romanticized imitation of a Mexican mercado, stuffed with overpriced tourista junk with a few dated historical signs and exhibits. The most interesting buildings there are closed to the public, and many don't have links to Hispanic culture...from the Italian hall (an immigrant social club) to the opium dens of the original L.A. Chinatown. You'll only learn about the real place (as opposed to tourista) if you get a pre-arranged tour from one of the park rangers, which is pretty much limited to school and professional groups.

There are all sorts of more interesting things for visitors in Downtown Los Angeles... Like Angel's Flight, Grand Central Market, the new Central Library (w/ its amazing escalator), Santee Alley in the fashion district, Phillipe's, etc.