The "value" of anything is determined my the individual and what it is worth to them.
As for art school, as others have said, it depends on what your goals are. It can be a means to career paths that require it, it can provide training is specific media, it can provide access to a network, etc.
For me, my college education (2 associate degrees, 1 bachelors, and 1 masters) were all job-related. I was a high school industrial arts teacher before I retired. After retirement I wanted to expand my horizons and challenge my aging brain and enrolled in a BFA program at the local university. While being self-taught in photography from the early 70s, and still working in film, I have now been exposed to other media and lots of history, visual theory, and criticism. I highly recommend this type of endeavor.
College can be expensive, as previously mentioned, but here in Montana, any resident 65-years old and older receives a 100% tuition waiver at all state schools, only paying the fees. My school also waived all the general ed requirements so I only take the art classes and, going part-time, I can graduate after 9 years for a cost of about $7,200. It would be less if I doubled up on classes but I am in no hurry. Plus, not only does it give me access to all the facilities, I am doing a study abroad with 11 other students in May when we travel to Sydney, Australia for the Sydney Biennale. The cost of the class, which excludes transportation there, but does include lodging, many of the meals, in-country transportation, entry into a variety of events, etc. is about $1,300. Going back to school is, for me, a real no-brainer.