I went many years ago. I was part of our nursing class student council, so the school paid for most of my expenses. I probably would not have gone otherwise. It is fun to meet other students, but mostly it is vendors that send up "classes," which are really designed to sell you things. At that time, there were a ton of hospitals there recruiting - from what I'm hearing it is tough to get a job as a new grad, so if you are flexible, it may be worth going just for that.
Years ago, when I was teaching in an ADN program and was the faculty advisor to our SNA chapter, a bunch of the students and I went to the national convention because it was being held in our state that year. The students had a great time and felt it was v. worthwhile.
I don't know if you would be refused entry if you weren't in nursing school yet but wanted to pay the fees to attend, but the NSNA (National Students Nurses Association) is an organization with chapters in individual nursing programs, and the conferences are generally intended for the NSNA members. Many schools have local chapters (the ADN program in which I was teaching had not had a chapter in the past, but some of the students started one up while I was there and I served as faculty "advisor" to the chapter), the the state organizations typically have an annual state convention and maybe some other events, and there is a national convention each year.