Is it patronizing or thoughtful to say "Gracias" to an Hispanic worker?

At my car wash, there are a number of Hispanic workers; I assume that most of them are from Mexico. After they are finished cleaning my car, I always say “thank you.” Sometimes, I think of saying “gracias.” I am ambivalent about whether saying“gracias” to a known Spanish speaking worker in the U.S. is gracious or would be perceived as patronizing. (I would prefer this not descend into a discussion about bi-lingualism and “if they’re here, they should speak English.”) Your thoughts?