I went last year with DS1 (who was starting school that September) mostly because I wanted to see who I might meet that could be in his class. I am going with DS2 (who starts this September) for exactly the same reason!
I am beginning to think it is more for me than them! It is a very good opportunity to meet some new mums and dads as you may find them invaluable as friends and 'homework confirmers' over your daughters first few months at Pates. I did rely on my new found friends to confirm that DS feeling tearful and a little overwhelmed at times was normal and happening to their kids too.
I guess it depends if you are interested in that kind of relationship. It is a nice chance for your DD to meet some others in a very relaxed atmosphere but also understandable that she might not want to miss her dance lesson.
My kids won far to many sweets for their own good last year and I had to help them to eat them!