Ginza is also of interest for its architecture, dining , tea rooms , entertainment and attractions.
Yes, the additive focusing modifier "also" (an adverb) is modifying (thus part of) the underlined preposition phrase.
"Also" is after "is" because it is part of the preposition phrase, which is subjective predicative complement of "is", It relates to the subject "Ginza", just like "Ginza is interesting / famous / a large district of Tokyo", and so on.
Incidentally, "also" is quite flexible in its position in the preposition phrase:
"Ginza is of interest also for its architecture … ".
"Ginza is of interest for its architecture … also".