"For example, the Field Museum in Chicago at one time welcomed more than 300,000 students every year. Recently the number is below 200,000. Between 2002 and 2007, Cincinnati arts organizations saw a 30 percent decrease in student attendance. A survey by the American Association of School Administrators found that more than half of schools eliminated planned field trips in 2010–11."
The article points out improvements in student recall, critical thinking, historical empathy, tolerance, and interest in museums.
Surprisingly, "One consistent pattern in our results is that the benefits of a school tour are generally much larger for students from less-advantaged backgrounds. Students from rural areas and high-poverty schools, as well as minority students, typically show gains that are two to three times larger than those of the total sample. Disadvantaged students assigned by lottery to receive a school tour of an art museum make exceptionally large gains in critical thinking, historical empathy, tolerance, and becoming art consumers."
If your own district had curtailed these trips, you may find that this new research is helpful in making your case.