Visited campus this week - I thought the island was beautiful and the buildings where actual classes are seem nice. Yes there are some old military buildings out there - but I did not mind it.
There is poverty in Vallejo. Crime accompanies that, but I did not feel unsafe there at all. I also toured some really nice gated apartments in Vallejo (more in the southern part). If I can’t find housing on Mare Island I am probably going to live in one of the complexes in Vallejo. I’ve heard of people who are even more concerned about safety living in American canyon.
If you want to end up in California, touro will set you up for that. I would personally hesitate to throw that away if that is important for you because of fears about Vallejo or because the classrooms on island aren’t in brand new buildings.