I think they are designed to be a nice bonus to the good explorer. They only get tedious when you've beaten the game and you are specifically farming them all to 900.Ya I think they're made to be ridiculously annoying to find. You only need a certain number, though, to max out inventory. Pretty sure it's 441, which is my goal.
I have roughly 200 so far and have only explored properly 1/3rd of the map. Just by gemeral exploring I've found them.
Though I will say the horse ones are a pain in the ass. As I'll never get them will I specifically come back later with a horse (which I never use unless the game forces me to to get something).