Some areas of Vista are nice, but I look at it this way – if you’re a delinquent living in a bad area, and you’ve got a choice of burglarizing your welfare recipient neighbor or the guy on the hill with the Benz, which would you pick? Seems like more of a target than an oasis. Also keep in mind what you have to drive through and look at every day, and where you have to shop (e.g., guards in the grocery stores).
That said, I lived in a questionable area of Vista for a year and never had any trouble. Maybe I was lucky. Shadowridge has managed to stay nice for 25 years.
Edit: not to mention a massively mismanaged local government. There are a lot of reasons San Marcos prices are higher, even though the location and weather aren’t as good as Vista.