Nick's comment about Gatsby's worth is an accurate one in that he actually earned all of his money, albeit through illegal means. "The bunch" Nick refers to here—Daisy and Tom—inherited their wealth. So in this sense Gatsby is worth "the whole goddamn bunch." However, the answer to this question is not that simple. Gatsby does some horrible things in the novel, particularly using his friend Nick in order to fet closer to his cousin, protecting Daisy after she runs over Myrtle, and attempting to destroy Daisy's family.
But in this instance, Nick might not be referring to Gatsby's wealth, rather his "extraordinary gift for hope" and "romantic readiness" that helped him turn "out all right in the end." However, this is not that simple either. While Gatsby had this extraordinary gift for hope, he became obsessed with a "foul dust" that "floated in the wake of his dreams." This "foul dust" referred to Gatsby's desire to be like Daisy, or at least worthy of her. This meant that, while Nick might see him as better than Tom and Daisy, Gatsby wanted to be just like them.
As a result, I would not necessarily agree with Nick. Perhaps Nick's praise of Gatsby has more to do with himself than with what type of person Gatsby really is