I can see both sides of this and have some experience with my now 19 year old son. First, your window is correct. After about 12, it's all about their friends and time spent with parents is a drag. The problem I have is that you have only talked about your dream. I'm not hearing that the family really shares your dream. Having been there, I can tell you that you don't need to necessarily do something grand to make great memories with your kids. When my boy was about 8, we started taking annual father-son trips to Vegas every summer. We'd get a suite at the Mirage and spend the week playing in the pool, seeing the sights, seeing kid-friendly shows like magicians, etc and just hanging out with each other. We had a great time and we both looked forward to it every year. If I were you, I'd check in and see what their dreams might be. It would be a shame if you spent their college money to go cruising only to have them one day say, "Gee Dad, I wish we could have gone to baseball camp together".