Yes, "Cuánto le gusta a Usted" would be necessary to differentiate the person, because the word "le" is a prefiz which indicates action affecting the THIRD person (he or she) and the form Usted is a kind of respectful protocol to name the second person (Tú = you) by using all the forms of the third.

For example:

"Cuánto te gusta" = "How you like it !" : there's no ambiguity, that's second person, familiar form.

"Cuánto le gusta" = "How she likes it!" OR "How you like it" : ambiguous.

"Cuánto le gusta a ella!" = "How she likes it"

"Cuánto le gusta a Ud." = "How you (respectfully) like it!"

Curiosity: The third person used in place of the second comes from the treatment of authorities in ancient times, but widely used to address parents in some regions, and it is the formal treatment for any person not familiar to us. The pronoun YOU was replaced by Vuestra Merced (Your Honour). Usted is a contraction of Vuestra Merced.

Curiosity II: My wife and I address ourselves as Usted with all the verbs in third person. She calls me by my last name and I call her "Señora". When we use the second person, it is a signal that something's wrong.

Un abrazo - Andrés