I am wondering if there exists a Vita collection that is already in VPK format ?
VPK is just a renamed ZIP. It was created for Vitamin, the first public dump tool for Vita. It was abandoned months ago and it dont produce proper dumps, even playable dumps in some cases.
MaiDump was the first dump tool for Vita (but released days after Vitamin) and it is far better than Vitamin making the dumps, it can dump updates, dlcs, games from physical or digital games.
But MaiDump use its own software to launch games and its own structure of files and folders. Thats why, i guess, No-Intro have converted them to VPK, it is more ... standar.
Pure VPK files (i mean, Vitamin dumps) are totally outdated and MaiDump must be used to ensure certain compatibility.