I wanted to visit SB this Spring Break, but I didn't get a chance. I grew up 15 miles away from UCR, so I went there occasionally to study.
Now for starters, I have this strange belief that it doesn't really matter which UC you go to, as long as you get a UC education. You could go to Riverside and study your but off, or you could go to SB and party. The university and education in general is just a school. It depends on what you make of it.
Also, this stuff about UCR being a low tier UC is just bull crapp. A UC is a UC, the undergraduate education is pretty much the same everywhere (of course with exceptions like Merced and Berkely). You are not going to a JC or Calstate. You just have to study and work hard, and you can do anything.
Like I said: a student with a better GPA and MCAT from UCR will beat the crappy student from Berkely.
By the way, UCR will have a medical school in a couple of years, SB won't. It was recently approved by the UC Regents.
Visit SB and Riverside, and see where you fit it, and where you will be in the next 4 years.
Best of luck.