WOW! You'd pay over $500 (for your party) extra for the NS? That pays for at least one (if not multiple) nights at a Disney resort. Not me!
To each their own.
I will too. I only get very limited time off work and the time is precious to me so we will pay more to get the extra time. I'm a crazy pennypincher so I weigh all the costs to decide if the extra time savings is worth it to me. For this next trip, it is. For some trips, not so much.
I check fares quite obsessively and while spirit is the "cheap" carrier out of DTW, I usually still end up on Delta due to prices and flight times. For my current trip, we got Delta tix for $150 per ticket and Spirit was quoting $300. Of course I could get it for $90 if I was willing to cut my trip short by a few days and fly midweek at inconvenient times.
But I try to fly close to the weekend after work and then return in the afternoon at the beginning of the week. This way I manage to squeeze 10 days at Disney with only 7 actual work days off.