The answer is Yes for the second question, about $(\exists x)(\forall y)w=1$. Following Christian Remling's idea:
If a sentence like
$$\exists x(\forall y)(yxy^{-1}x^2y^{-9}\dots=1)$$
holds in all finite groups then it holds in $\mathbb Z/n\mathbb Z$
where it just says (for certain constants $a,b,c,d$)
$$
(\exists x)(\forall y)((a-b)x+(c-d)y=0).
$$
The only way this can be true is if $c=d$.
So *the exponents of $y$ in $w$ add up to 0*.
In that case, the sentence is true in all groups because we can take $x=e$.