Well I can't really speak for the Austin Campus but the San Marcos campus I can comment on to an extent. I've only been there once, which was for the interview, but they did give us a tour. I wouldn't really define it as a true campus, like let's say a UCLA or Stanford, but then again you can't really compare it to schools such as those since St. Augustine is home to only a small handful of programs. The San Marcos campus is situated in a residential area. It is made up of 3 buildings, each of which are only 2 floors I believe. During the tour we were told that one of the buildings was going to be under construction. They're renovating the space to accommodate the growing programs. The facilities itself were pretty nice though and more that adequate for a proper education.
The real plus for the San Marcos campus is that you'd be in California, or more specifically, southern California. The weather is pretty spectacular year round. You're looking at 70 degree weather minimum 90% of the year. You'd be about an hour or less away from anything awesome like San Diego, Los Angeles, Disneyland. You'd be 20-30 mins away from the beach. 4 hours drive from Las Vegas. You can even hop on a plane and fly to San Francisco or even Hawaii. The fares are super affordable. I can go on and on.
Ok that's all I got. Hopefully someone can shed some light on the Austin campus.