I would offer a slightly different perspective, which is to consider the enrichment that she will carry with her for the rest of her life. It's not just about fun in the now or future "advantage." Same with a college education, you come out of it a different person, whether or not you "use" it in a practical sense.
It sounds to me like this opportunity is very high value in terms of enrichment. Of course, that has to be balanced against your particular family's financial circumstances. Considering your retirement and not being a burden on your children is also important!
My thoughts exactly. Obviously you don't want to bankrupt your family, but IMHO these young years are fleeting for our kids and any positive, enriching experience (that they want and seek) are worth supporting. My DH is very much of the "how much money will she get back in wages" mind set, and I disagree... for me it would be about the positive experiences and learning for the child (confidence, self-esteem boosting, etc).
I was in guitar lessons from the age of 9 (and was really good at it) and also took voice lessons after high school. I've never earned a dime from my musical talent, but it's definitely enriched my sense of self.
On the other hand, if you have a "future career value" perspective, you can always look at the transferable skills, like commitment to task (practicing), presentation (performing), people skills, etc.
If you can afford it, $400 seems ok to me. I've spent that much putting my two in sports (for DS8 it was even almost like sensory integration therapy) and I've never regretted it.
