I'm nowhere near a spend-thrift, but I'm firmly pro paying for convenience in almost any circumstance (and almost at any price.) When you factor in what my "time" is worth, and then factor in the opportunity costs, it's almost always a good value. The decision on whether or not you want to allocate your budgeted funds or take a principled stance is another story.
When you think about the all-in cost of a day at a Disney park, where your main objective is to at least experience that one, 3-hour wait time ride, you're devaluing the rest of the park and over-paying for that one ride. Paying $50 more, per person, to get back 2.5 hours of time in the park re-balances that, and probably even makes the overall cost more valuable.
Better way to think about it, assuming your objective is to experience the most attractions in one day at one park:
- 25 attractions (rides, shows, character encounters, etc.)
- 10 hours of park time
- $600 all-in cost for family of 4
Let's say no "extra" fast pass means 3 hours at the big ride and all the other attractions average 30 minutes. You're doing 15 things for $600 ($40 per attraction.)
With $50 add-on, all the attractions average 30 minutes, so now you're doing 20 things for $800, which is still $40 per attraction but you've done 33% more things to better maximize those 10 hours. If missing some of those extra 33% more things would have meant going back to the park a second time (at additional dollar cost, or even just the time cost where you can't do another park instead), that's making it even more worthwhile.
I'm usually a tight-wad, but there's two things I value more than money: my time and memorable experiences. It's why I'll always spring for the VIP/Meet & Greet experience for the kids if we're goign to a Yo Gabba Gabba or DanTDM show. And why I'll redeem my credit card points to work the goalpost nets during an Eagles game or season-long VIP parking that saves me 45 minutes of traffic after the game, instead of cash back.