I see no problem with it. Once ours hit about 15 or so, we turned them loose if they wanted. But WDW is the only place I feel comfortable doing so. We used these guidelines:
1. Age is less a factor than the individuals. We know ours are smart, and have been taught proper conduct.
2. They are clear that the rules are non-negotiable and zero tolerance. Even one minor violation completely removes this privilege.
3. They each have cell phones and are required to keep them on and pay attention to them. We reserve the right to call any time, and as frequently as we want, and they must answer. If on a ride or show, they must call back as soon as it's over.
4. On-their-own time is limited; most of our time is spent together as a family; getting away from us is the exception, not the rule. If that gets to be an issue, perhaps it will be time for me and Momma to go alone and leave the kids home- or they could pay their own way. Thankfully it's not yet an issue, because we still have a lot of fun together.
5. They will re-read and remember guideline #2!
Being that they have been taught correctly, their cards have charging privileges, so they can feed themselves; any other purchases require a phone call for pre-approval. This has worked with zero problems.
Only way this won't work is for folks that have neglected to give any discipline to their kids as they grew up. In that case, all bets are off!