To get the most out of your money, go with Private or Semi Private lessons. Kids attention spans are typically low once the group gets over 10-15 kids.
If your kid has a hard time paying attention for an entire skills session, he's too young to be doing extra skills. Not a knock, I stopped sending my kid once I realized it was just throwing money at extra ice for the sake of extra ice. He should get enough if you are on a club team and he maintains focus on his team practices and skills. But when he comes asking for more skating, by all means send him.
It's an arms race at the younger ages and too many parents are wasting time and money on extra skills for players that are too young to realize why the extra work is worthwhile (and ultimately necessary to compete at the higher levels).
So I guess I'm agreeing with you that private/semi-private are more beneficial for younger kids, if you really want them on the ice more frequently than everyone else.