Seems somewhat underpowered. Given that green gets Naturalize at which is an instant and can hit artifacts too, a sorcery-speed Demystify certainly shouldn't be more than 1 mana, and the Battlegrowth isn't usable as a combat trick so certainly shouldn't add more than 1 mana.

I designed a similar card in Clockwork Wings: Repurpose. Given that it's sorcery-speed, I think 2 mana for Naturalize + Battlegrowth is fine.

How does it look now?

Mmm... probably fair; but often it'll be irritating, if there's no enchantment available to target and you just want the +1/+1

Maybe not a problem? Unsure. Wording it to avoid that ends up horrid.

True; it'll also be irritating if you want to destroy an enchantment when there aren't any creatures out.

The wording that avoids both of those is "Destroy up to one target enchantment. Put a +1/+1 counter on up to one target creature."

And yes, I reckon this is fine at just .