later on why not at the other girls to starmaker and manage them? Could be fun. Have be an alternate ending sorta thing or a new game plus. Just an idea. 

I agree, there are still interesting characters that you can't talk to, some can be seen in Mario's quest, there is also a girl in the background in the park. As for the background, after you have made Alice only yours, she always appears with some man on the beach, in the background. Attention to detail and fans are the key to success.