As the other posters have said, one needs to find the right group however, the 'grading' of a tour can help. I did an Iceland hiking knitting tour and it was fun (a lot more hiking than knitting and graded as the most strenuous). I ended up making a friend who invited me to visit her in the northern Netherlands (I just returned yesterday). Had a blast. I think that we were both fairly active people who also like yarn and knitting/crochet made the experience fun.
She's also an avid hiker and has been to Scotland 40 + times - we are going hiking for two weeks in Scotland next year.
I've also been on cruises (the ultimate 'tour) - the cruise line you pick determines the type of people and cruise experience.
I do a lot of DIY travel - I have friends all over the world and have been invited to visit (and vice-versa). That is the ultimate as they help you with local/regional information and many times offer to let you stay with them.
I've also done tour trips with a travel group from Meetup-the comment made that the tour organizer is usually doing it for a free trip is spot on. If you know that, you can adjust your expectations. The two trips I did were a ski trip to Alaska and a hiking trip to Havasupai, Grand Canyon. That particular Meetup travel organizer made going to both of those locations easy for me - I paid the amount and showed up with my gear and went on the trip. I didn't do any logistical planning, which was what I wanted for those type of trips.
Finding companions of the same fitness level, educational level, etc, is also of concern. Nevertheless, I've found that while traveling one meets very interesting people and if one talks with the locals, one can find out a lot of great information: what to see, what not to see, best deals, best restaurants, what is the best feature of their regions, etc. Makes for a much more enjoyable trip.
Lastly, I haven't done any traveling with an alumni group, but my parents have. They've enjoyed those trips as well. I think it depends on where you went to school as to how much you might enjoy the trip and companions. I'm intrigued by the comment made the empty spots could be filled by non-alumni. I might try that someday.