most of the peak-requiring unlocks are either cosmetics or modifiers
usually there are collectables in the map that you need to pick up to get peak ranks (but then theres 2-10)
i believe that you dont NEED to get peak ranks to unlock every level (minus P-levels), just a good rank average
a pretty good handful of peak ranks are probably required to unlock the P-levels, but after finishing the game you unlock the ability to auto-restart levels if you dont get a peak rank on them, which is very useful
