Yes it is technically an option, but so is ordering the most expensive thing on the menu. People do it because they can and because they perceive that's how they get value from the plan. I doubt it will be different with the alcohol. People who normally wouldn't drink will get drinks because they can and it's a a great "value".
Well I was far and away when that happened, so what I didn't know didn't bother me.
then don't let it bother you now. nobody's forced to buy the plan, and nobody is forced to order the most expensive thing in each restaurant. if everyone did that to maximize the value of the dining plan and actually access the "savings" advertised by Disney, there wouldn't be much incentive to continue to offer this. especially for the parties staying in a value resort with enough people that the free dining promotion is actually a great deal, they probably aren't feeling the pressure to extract every ounce of value from the dining plan.
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there's a small number of people (who all seem to congregate on the DIS) that actually crunch the numbers before and after using the dining plan to determine whether they made a "good" financial decision in purchasing. but once vacation ends, *everyone* realizes it's a sunk cost. at most, doing a post-trip analysis will probably inform the person's next visit, but plenty of people will not pore over their receipts after their vacation precisely because it's over.
more to the point, sunk costs are exactly why "free" dining and the dining plan in general appeal to people: pre-pay your meals except tip, and then the price "doesn't matter" when you're in the restaurant. lots of people on these forums will post trip reports and admit the dining plan cost more than it would've OOP, but they wanted to try it, or they liked the freedom in ordering, or it was just a nice safety net to know they could dine just about anywhere, or they were ambitious and thought they could order steak forever. but they know during their 5-day, 7-day, 10-day trip that they are not ordering steak 2 times a day and are losing value on TS credits or wasting snack credits. and the freedom of sunk costs frees them from caring, because why should they? the money's already long gone; might as well order what you like. and maybe pay a lower tip on a $30 (instead of $50) entree.
I would believe that a majority of people would change their behavior to always maximize value on the dining plan if it worked like this:
> you still pay for the plan ahead of time, but get a refund for any unused credits after your trip ends.
> if you use up all your credits - whether you "under spent" the value of each credit or maximized - you don't get a refund.
in that situation, paying attention to price would be on many more minds than it is now. it's still a sunk cost, but with the dangling carrot of ~money back~!
since the dining plan doesn't work that way (and never would), and I highly doubt most people come back truly maximizing of the plan, I also don't believe that this will suddenly force everyone to buy more alcohol.
the people who *really* wanted to drink on the dining plan before, did. they paid OOP.
the people who *really* want to drink on the dining plan in 2018, can, and more power to them.
the people who had a take-it-or-leave-it approach to alcoholic beverages before, might drink. might not. might just act like they would outside of Disney and order a beer if they feel like it.
the people who reaaaally wanted to drink on the dining plan before but refrained because they didn't want to spend OOP and they did all of their dining plan calculations ahead of time, can finally get a jack with that coke. (or whatever.)
the people who don't drink at all can order a milkshake.
and the people who simply do not worry about maximizing the value of each credit, will fall somewhere into one of the above categories.