Theres good diversity and theres bad. And Im not just talking about tasty "ethnic" restaurants etc.
I'd argue that you
are mostly talking about ethnic restaurants.
Abject conformity is stagnation, which manifests in every way: art, tech, science, even personal experience of the world, approaches to nature, and so on.
Surface Culture: Observable and palpable elements such as food, dress, music, dialect, and holidays. They are characterized by low emotional resistance to alternatives. Accepting alternatives does not create great anxiety. I can easily prefer lasagna to chitterlings without feeling that I've "abandoned" my own culture. Maintaining diversity in surface culture causes very little social disruption.
Shallow Culture is made up of the unspoken rules around everyday social interactions and norms: Courtesy, attitudes toward elders, nature or friendship, concepts of timeliness, personal space, rules about eye contact or appropriate touching. This level has a strong emotional charge. Interpretation of certain behaviors can manifest as being friendly, hostile, disrespectful, or offensive. Social violation of these norms can cause mistrust, distress, or social friction. This is where fist fights occur.
Deep Culture is the tacit knowledge and unconscious assumptions that govern world view. They include cosmology, morality, spirituality, health, and theories of group harmony. Deep culture governs how we approve of new information (epistemology). While shallow culture pertains to how moral values are socially presented, deep culture pertains to how those moral values are characterized. Deep culture defines right/wrong, respect/disrespect, honor/dishonor. This is also where we can run into deep social discord when cultures clash with long-term and extreme physical violence at the deep level. This is where riots occur.