well they probably have the same importance. i was thinking that terra put his heart/memories into riku, aqua to kairi, and ven to sora. they are all three important characters, like how SRK are the three main characters. and did anybody see that scan of BBS? vanitas's keyblade has eyes in it that looks like riku's soul eater and road to dawn keyblade. i doubt they have any connection though. unless vanitas is some sort of older clone of riku, which i really doubt. and maybe it's like what lycorismoon29 said, it's like past, present, future type stuff.