Isn't ammonium chloride more electrically conductive in water than acetic acid would be, because ammonium chloride doesn't dissociate well in water and acetic acid does?

Nope, what you've said is completely backwards.

Ammonium chloride IS more electrically conductive in water than acetic acid, but it is because:

• Ammonium chloride is an IONIC compound, which contains a polyatomic cation that DOES dissociate in water.
• Acetic acid is a WEAK acid and therefore DOES NOT fully dissociate in water.

AMMONIUM CHLORIDE

#"NH"_4"Cl"# dissolves easily in water:

#"NH"_4"Cl"(s) stackrel("H"_2"O"(l)" ")(->) "NH"_4"Cl"(aq)#

and breaks apart into ions easily in water:

#"NH"_4"Cl"(aq) -> "NH"_4^(+)(aq) + "Cl"^(-)(aq)#

while #"NH"_4^(+)# also partially dissociates in water:

#"NH"_4^(+)(aq) + "H"_2"O"(l) rightleftharpoons "NH"_3(aq) + "H"_3"O"^(+)(aq)#

ACETIC ACID

On the other hand, #"HC"_2"H"_3"O"_2# only partially dissociates in water:

#"HC"_2"H"_3"O"_2(aq) + "H"_2"O"(l) rightleftharpoons "C"_2"H"_3"O"_2^(-)(aq) + "H"_3"O"^(+)(aq)#

The equilibrium lies strongly to the left...

And thus, #"NH"_4"Cl"# easily conducts electricity as #"NH"_4^(+)(aq)# and #"Cl"^(-)(aq)#, while #"HC"_2"H"_3"O"_2# comparatively does not do so well...