My 30th High School reunion was this last summer. I did not go for several reasons. For starters, though my high school days were not awful...in fact, I have many fond memories of the time, I have stayed in continuous contact with just one classmate since then. I don't need a reunion to maintain that friendship. From a viewpoint of prioritising time and money, I would much rather explore Italy than reliving "Glory Days" with people I haven't talked to since I was a teenager! :-)
I just didn't have the long-lived connections that they had with each other. I went to high school in a small town in Montana and most of my classmates were born and raised in the area and still live there. They all started school together when they were 5 years old. I moved there when I was a freshman, and left 4 years later to go to university and never returned. My family no longer lives anywhere near the area, so a visit to the reunion would be vacation/holiday time and money that would be better used visiting my family or friends who are an important part of my life now.
I got some emails from the reunion organiser and some links to some YouTube videos. It was kind of strange because I really didn't recognise a lot of them. And I was in a small graduating class of 30 people, so I knew them all. But it reinforced that I made the right decision not go and spend the weekend small talking with a bunch of strangers and instead spent the money on spending Christmas with my family.