One call a year from the place you spent your formative times... that doesn't sound too much.
I agree. Unfortunately, if graduates finish up feeling glad it's over (and feeling animosity to the school for the way they've been treated) even that one call a year can be too much.
Last year HK-UST invited three year alumns to a reunion, but when they arrived they realised it was all about the Financial Times rankings questionnaire which was about to be sent to those who graduated 3 years earlier. At the "reunion", HK-UST asked these recent alumns to say good things on the questionnaire.
I know for a fact many of these alumns were upset they hear nothing from the school for years and then they get invited to a function where they are told how to fill out a school evaluation. Hardly ethical and hardly consistent with building a strong alumni body which connects to the school in a manner which helps current students.