from our reader stand point:
child Raki:
manga shown him traveling around with Clare, helping her in many various ways.
child Raki = significant for both the characters in the story and us the readers.
adult Raki:
manga hardly shown him traveling with Isley+Priscilla, and then just Priscilla. Helping Priscilla (and slightly Isley, and the rest of the island) in an abstract/indirect way. He also killed a normal yoma. he's a character of interest (as Yagi surely has stuff planned for him), but as of yet, adult Raki is not significant, but that can definately change soon...
adult Raki is significant for the characters in the story, but not for us, the readers.