If it is possible to visit one of the campuses on your list and spend the night, it is definitely a worthwhile way to get a true sense of the full student experience at that school. The campus tour and college "quick facts" can be helpful as a place to start, but spending more time as a potential student (e.g., in an overnight stay) can help give you a much better understanding both of the school itself as well as of college in general.
In terms of preparing, I would suggest thinking about what you are looking for most in a college, and assessing these factors during your visit. You might do some research beforehand about the things you'd want to be sure and experience (e.g., an academic class, the cafeteria, a basketball game) and seeing if you can make these happen during your visit. If possible, I would also suggested trying to stay with a student that most closely aligns with who you are and what you are looking for in a school and in the college experience. This might be a student with a similar major interest, extracurricular interest, hometown, etc.
With all of this said, overnight stays might not be doable for all students because of scheduling, financial situations, or something else, so I would put these experiences in the important category but not necessarily a "must do."