If by "all-Vig masters" you mean the Smart Studio Sessions that would be on disc 2, and also "The Devonshire Mixes" which would be on disc 3 (a lot have been omitted); i could say you won't find a result as polished as the final version since Andy Wallace's work is really evident on the album, but it's also true that Nirvana was certainly going after a cleaner sound, as opposed to what they had done on "Bleach", for instance. The January 1, 1991 session at Music Source Studios in Seattle with Steve Fisk at the helm, is proof of that. In conclusion, there is some amount of grittiness in that material but it's not radically different all things considered.
Despite the redundancy of its inclusion, the recording of Nirvana's performance at The Paramount in Halloween of 1991 is, from my point of view, the most valuable thing this re-issue will have to offer, but it just won't save this artifact from being a very disappointing release.
Religion kills more than it saves you, man...