I'll be honest I was straight average. To me it's totally worth it. You would be surprised how many memories, that you're truly a part of. For example my senior year 9/11 happened. That was a memory we all shared. Many more memories like that too.
Facebook can be Fakebook some people on my FB haven't uploaded a new photo since 2008.
Really it depends on your mind set though. If you're going to grind an axe with someone don't go. If you're going intent on getting with someone don't go.
Basically keep your expectations low, and acceptance high. You might get revenge. You might hook up, you might forgive, might laugh with or may bond with people.
At my 20th a girl told me she had a crush on me back in high school. Not going to lie that was bittersweet, on one hand I was flattered. On the other hand it's like damn if I knew we would of had fun.
At my wife's 10 year reunion an ex couple hooked up again. Engaged 6 months later, married a year later. It does happen more than you think
I can go on, but I doubt anyone reads this plus the rest of my experience is common place.