I dearly love Vincent, I just don't think the show would've been the same without him.
He's actually played pretty crucial roles, especially in the first series. He works as emotional support, as he helped Walt with his mother's death and was a companion to him before he was kidnapped. He also helped Shannon cope with Boone's death and gave her a sense of meaning when Walt asked her to look after him.
There's also quite a bit of evidence that Vincent's "magical." He led Shannon to Boone's grave towards the beginning of the second season. And recently he led Charlie to Sawyer's stash of heroine, therefore letting Charlie truly rid himself of his addiction.
mrgreen