I know this probably does not help much, but personally all these could be dropped and I would not miss them at all:
Array Helper
CAPTCHA Helper
Date Helper
Email Helper
Form Helper (except form_open)
HTML Helper
Inflector Helper
Number Helper
Path Helper
Smiley Helper
String Helper
Typography Helper
XML Helper
Security Helper
And most of form_helper (apart from form_open for CSRF reasons, that is really helpful).
I think a good case can be made to get rid of helpers altogether.