Unfortunately no recommendations for nice dine-in places, but for quick bites, I worked in Pleasanton and Walnut Creek for a bit. The mall right across from Kaiser Pleasanton is probably my favorite poke place (Go Fish? or something like that). The outdoor mall across by Kaiser Walnut Creek has a good place called Heritage Eats which is pretty much a swankier Chipotle. Its similar to Chipotle only cuz they make burritos/bowls in front of you that are also customizable if you want. Not really Mexican, more of an Indian/American/Thai/Vietnamese mix I think.
Also unrelated, but that outdoor mall is also just a really nice place to shop and walk around. Essentially the Stanford shopping center of the east bay. Livermore Premium Outlets are not bad, but I feel like it'd be a disappointment since I'm sure you have plenty of experience with the better Vacaville counterpart.