The link below returns a terrain map of South Marin. As you can see Mill Valley includes a valley bottom and slopes up to ridge tops to north, west and east. Consquently understand that Mill Valley is a composite of neighborhoods with micro-settings that vary within short distances and result in different landscapes and micro-climates. Generalizations have so many exceptions...
There are different neighborhoods and, to try to put it in perspective, values range from a bit under $1M to, well..., off the board. Most "neighborhoods" vary in value/quality and small homes, large and estates intermingle.
The character of the community is probably best exemplified by the downtown village and park at the square that is casual, upscale and sophisticated. Decades ago Mill Valley was more of an artsy, hip community and still retains much of that flavor and continues many cultural events such as music and theatre.
The map below can be changed to air photos and zoomed in to. Then one can obtain street views. There is a bit of a learning curve but you've in hand an excellent tool to help learn more.
I'm happy to discuss neighborhoods/communities of Marin, their characters and nuances of difference - actually I love to. Hopefully you'll find useful tools on my website, http://www.realtz.com. Be in touch if I can help.
Residents do maintain their properties very well and almnost anything grows here so you often see very well landscaped yards.
There are dramtic differences between neighborhoods. Many ore on steep hills with great views and others ore in the valleys in between which is great for kids and their bikes.