...but christians who claim that the value of christianity is that it leads to success in life -- earthly life -- drive me nuts.

Well, they probably wouldn't put it that way if you said it like that, but I agree that this is how it comes about. Probably if you cornered an "elder" in my community, they'd say that Christianity is primarily important for the soul.

But at a parenting talk I was just at, someone commented that "next to raising your kids to know the Lord, loving your spouse well in front of them is the best thing you can do."

I probably didn't define "fail" very well -- I think they mostly mean that the Christian child will grow up to have better values and morals, not necessarily more money, prestige, or the like.