How does Nick's statement "You're worth the whole bunch put together" show a change in Nick from the beginning of the novel?
Among other things, the statement shows just how much Nick has been sucked into Gatsby's world, like so many others before him. Previously, there'd always been an air of detachment about Nick, a sense that he was somehow above the fray of Gatsby's strange, exciting world. Yet even he has succumbed to its charms, drawn in by a combination of Jay's charisma and the fundamental decency of his character.
By complete contrast, Nick utterly rejects the world of Tom, Daisy, and Jordan and the shallow, vacuous phoniness it represents. He respects Gatsby all the more because he's not really one of them. Gatsby is an outsider: someone who'll never be accepted by the old money elite of East Egg. And for Nick, that's something to admire. Although Gatsby may mix socially with such people, and although he clearly aspires to be accepted by them, he still retains some integrity.
The key word in Nick's statement is "worth." Gatsby may not have been born with a silver spoon in his mouth; he may have derived his phenomenal wealth from the proceeds of organized crime; yet for all that he's still worth a whole lot more than all the Toms and Daisys of this world put together. Nick has changed, because thanks to his relationship with Gatsby and his negative experience of running with the East Egg crowd, he's finally realized where the true worth of someone really lies.
I would say yes, in that in the beginning of the novel, Nick is very careful to state how he reserves judgment. His father reminds him that not everyone was brought up with the advantages that he enjoys, and the values that were instilled in him. He doesn't judge people, and tries not to hold their shortcomings against them.
This is a stark contrast to the way in which he has made a total judgment of Gatsby. Rather than passing a negative judgement or making a stereotype, he has judged Gatsby to be a good person, and tells him so. In so doing, as well, he has passed judgement on Tom, Daisy, Jordan, Myrtle, and George... stating that Gatsby was worth all of them put together.