As is Rangers can deal pretty significant damage with the right build on single targets, I really dont think they need any buffs on the elemental arrows in addition to that.
I don't mean to say that rangers need a buff. It's the opposite in fact. I think every one else should get less benefits from special arrows, and they should remain as powerful as they currently are only when used by a ranger, provided the player succeeds a tinkering check; so, one more opportunity to get a dice roll, really
Effectively, it's kind of a buff to the ranger if everyone else gets nerfed, but it's on such a niche aspect of the game that I feel like it'd be a nice touch. Doesn't really change overall balance.
And as was mentioned earlier, arrows cost a significant cost and are pretty rare so it wouldn't be that much of a nerf anyway.
