I think there could be community-driven lists of collectibles instead one fixed. Item type for any collectible is “misc item” so generating these items to world does not affect game balance.
This way anyone can have the possible things to collect they exactly want - like when you name your favourite fruit in nethack. Also this eliminates clutter because you can shut down categories you dont want to be generated in world.
Lists are handled in generalized way, so item in list A has equal chance of spawning to item in list B, and the rate of spawning is dictated how many items in total there are. This way chance to find item you are looking for is equal no matter how many collectibles-list your game has, the more you have the more game generates clutter, but chances of finding one particular item is always the same regardless how many or few collectibles lists you have.
Maybe the lists could allow tweak of in-category rareness, so you could have really common items from category or super-rares, but as average lists would be always equal.
This would solve the “That stuff is not important to me, but I want this stuff”. Just do your own list of wants and youre go.