I think raising children bilingually primarily happens at a very young age, indeed at the age they are acquiring (not learning) language. They aren't making decisions for themselves really. You may as well ask them what language they'd like to speak now they are starting out. (answer unintelligible gurgles)
Parents make lots of decisions for their children. What school, what religion, what values, what they eat, when they sleep (or go to bed rather), etc. etc. all with the best intentions and trying to do the best for the child. And not always according to a child's desires. It's a benign dictatorship. (But for a commentary on how successful it all is search for Phillip Larkins poem, This Be The Verse.)
By the time it becomes an issue of being a school type subject would be around the time they can decide for themselves and live with the regrets later (or not). And yet is making your children practice kanji any worse than making them practice piano or violin or making them clean their room and eat their vegetables?
I'm not sure if it would give children an economic advantage later in life. Maybe. Maybe it'll save them a few years study; what the economic climate would be in 20 years time is anyone's guess. Broader values and a wider outlook on life might be better than any specific language. (I'd bet on Chinese myself) And exposure to both cultures and languages might make them less parochial in their outlook.
Regardless it is their heritage and they deserve an effort to give them access to it as a child. Both cultures.
It's also about the parent. I would be very sad if my (potential) children couldn't learn a bit of Irish (cupla focail) and have a native grounding in English, but instead were exclusively raised through Japanese. I'd also be very sad if they couldn't have a native grounding in Japanese and experience Japan and their relatives as a child.
I think it's natural to want to share your experiences and language with your children.
BTW have you seen this?
http://www.omniglot.com/language/articl ... lkids1.htm
there's also a lot of interesting links there.