Make this a more interesting choice for rangers by doubling the level of the spell that the ranger gets.
Ranger 1 (L 4): Summon Nature's Ally II
Ranger 2 (L 8): Summon Nature's Ally IV
Ranger 3 (L11): Summon Nature's Ally VI
Ranger 4 (L14): Summon Nature's Ally VIII
And revamp with 3 choices per level like summon monster. I believe at high level, elementals are allowed.
This is all work that will need to be for druids anyway. Just roll it out earlier.