I hope I don't sound antagonistic! It intrigued me that you equated vacations with college.
Not at all. I like debating big-picture type of things. Hearing the opinions and thought processes of others forces me to think through my own points and adjust. A few years ago I was firmly in the "skin in the game" camp and worried about making sure both of my kids had exactly the same dollars available to them. After all, my parents couldn't give me any money towards college and I found a way to graduate debt-free, so dammit my kids should be able to as well. I've moved off of those points based on my personal experiences, research, and some of the arguments presented on this forum.
As I pointed out, the FAFSA determines an EFC, expected FAMILY contribution. The government calculates and public schools factor my parental contributions into the aid package they will present to my child. While I am not legally bound to provide the amount that the government expects me to provide, my kid can't just demand that the school revise their offer to include more grant money because daddy won't pay what is expected of him. Like it or not, until your kid can be treated as an independent adult in terms of financial aid, you're tied together. Maybe that's a better argument for why 0% parental contribution when >0% is feasible is not OK, in my opinion.
I have no beef with those who decide to essentially cut their kids off financially after high school graduation (assuming the child is 18), or set some max contribution level for college to help wean them off parental support. I don't know them or their kids, and I am not going to tell them how to raise their kids or spend their money. If my financial situation was different, I might still think that is appropriate. If my kids are total screw-offs, they aren't getting any of my money for college, even if I'm a billionaire. However, barring some very bad luck, my wife and I will be in the position to help my kids with their college tuition expenses without sacrificing our retirement plans or financial security. Selfishly, knowing that I gave them that gift, whether they ultimately appreciate it or not, will bring me a sense of accomplishment and pride.
Should my children be self-sufficient and not rely on my assets to fund their lifestyle as soon as they graduate college? Absolutely! Am I worried that by providing the opportunity to finish their Bachelor's degree debt-free will somehow derail that and they will be doomed to poor financial decisions for the remainder of their adult life? Absolutely not. My point about vacations, braces, etc. is that you're taking that same leap of faith from the day your child is born until the day they leave the nest -- you are spending money that you are technically not required to in the hopes of improving their quality of life. You did so without any expectation that they'd appreciate it or contribute financially toward it. If you've done your job they will appreciate college assistance at whatever level you are able to provide, and that switch isn't magically flipped the day the calendar turns to their 18th birthday. Knowing that a college degree is essentially a requirement to get any sort of good paying job nowadays, you've been spending money beyond the bare minimum to help the child out for the last 18 years, by not contributing at least the EFC you are effectively harming your child's financial future,
and you have the financial means to do so, I find it completely illogical to pick funding college as the point you decide to cut the kid off or use it as a learning opportunity about loans and debt by essentially forcing them to take out a loan.
As far as your question on how long to pay for vacations / whatnot for your adult children, I think the answer is 'it depends'. Assuming I have the means and I enjoy spending time with them, I will probably help subsidize family vacations. If I want to take the grandkids to Disney (I know, I hear the groans already), and one son can & wants to pay for himself and his wife but the other one can't afford it, I'll probably just pay for the 4 adults as well. The instant one of them demands that I pay for something, the free ride ends. I am happy to be generous, but it stops being generosity when it's a requirement. My mom likes buying my kids outfits and small toys all year long 'just because'. She and my dad are on a very limited income and I would much rather they save their money or at least spend it on themselves, but they choose to buy for my kids. I'll probably want to spoil my grandkids as well.