Good luck as you work through this decision.
I am a Walnut Creek resident, and I'd be happy to share my experiences with you, hopefully it will help.
I love it here. I have lived everywhere from places as urban as Boston to good ol' Shasta County, CA which is very rural. In terms of diversity and amenities, Walnut Creek has a decent amount to offer. No, it is not a major city, but for being a "suburb" it has a lot going for it, and all the amenities of the city a short BART ride away.
I don't personally feel as if everyone looks the same here, and have seen a lot more diversity here than I have in most places, and I have the pleasure of working with and living near folks of all backgrounds and walks of life. I think diversity IS what makes a place nice and livable, and after spending several years in a rural area, I wanted all the diversity, culture, and progress I could possibly get, plus I also wanted some space for my dog, and my own pool and garage. That said, I am very satisfied with Walnut Creek. I am a "city girl" at heart as well, but I don't miss the city so much because it is still very close by.
Walnut Creek has great food/shopping/dining and is also close enough to the city that if I want a little more of an urban feel I get on Bart and I'm in the city in 25 - 30 minutes. When I'm all shopped out, so to speak, I return to my backyard, swim in the pool, frolic with my dog, enjoy my backyard and garden. I really couldn't ask for more.
When we decided to buy this summer, we were looking in the Lamorinda/Walnut Creek area for an older home that had some original character. Cosmetic fixers were ok, because we are both really good at doing that work ourselves and wanted to be able to customize our home. We found exactly what we wanted, in excellent shape, with all the important upgrades (kitchen and bathrooms) but still with the mid-century appeal we did not want to compromise on, and structurally sound. We stayed in our price range, in the neighborhood we sought. Only a little work was needed (paint, flooring, etc,) and we have throughly enjoyed doing that work, and watching it pay off in a lovely home that is truly *us.*
Your preferences may be different from ours - but there is something here for everyone.
Somebody mentioned the "sulfur pits" near John Muir/Heather farms. As it happens, that area is exactly where we wanted to live, though we were familiar with the sulfur pits. I have a ridiculously acute sense of smell, and the only time/place I can notice it is driving down Ygnacio, right in front of the hospital. It's about a block long stretch, and while not the best aroma in the world, it's harmless. Don't let that steer you away from this area if you find something you like. The smell is not noticeable in most areas, and it's merely unpleasant to some, not harmful to your health like the refineries you have mentioned that you don't want to live near. We can smell nothing from our house, and we're close to all the things we love, so we weren't going to let that that dissuade us. Also,we are in the Northgate school district which is great for resale.
There are some really good deals in WC right now, many between 700-800. We saw some great houses in that price range in our search. We just bought our place a couple of months ago, and there's still a lot out there, in many different neighborhoods.
Personally, I can't say enough good things about Walnut Creek, and I recommend it if you want to get out of Benicia. It's really very nice, with good schools for your daughter.