My group does Stay and Scream every night we're in town at Finnegan's (yes, insert jokes about the Finnegan's people). We go a good 30min before the park closes to get a table, order full meals and several rounds of drinks. We run up a $200-$300 bill each night depending on how many adult beverages we have. We're HOPING to go 5 nights this year ASSUMING they have the ROF+Express we always get. So between the time the park closes, to the time of the event starting, we'll probably be dropping $1,250 in park during our time there. Not an insignificant amount of cash from 6 guys.
We also buy APs so we get free parking, can do the parks in the day, and get a discount on Merch. That's probably $350+ each for that pass. Then we all buy the RoF+Express so probably another $350+.
And none of us live anywhere near Florida. So those tickets are really only for 5-7 days per year. So we're each paying at least $100 per day that we are at the parks on tickets only. Then at least $100 more each for food and beverages. Then tons of merch and some of us doing the 6-house UTH tour. We usually go to Pat O'Briens a night or two after HHN. So that probably averages out to about $250-$300 per HHN day/night for each of us.
If they got rid of multiday tickets, I think we'd probably only do 2 nights (with the possibility to buy another one if it's super awesome) with no express and then probably buy the SeaWorld pass to go 3 other nights for $80 and blow all kinds of cash on drinks and food there. Instead of an AP, might just get one of the 3-day 2-park passes that you can get on Tickets at Work for under $200. Don't really need the AP if we aren't doing Stay and Scream every night.
That's just one group, but a good and accurate outline of how the lack of multinight tickets would affect the amount of cash we dump into the parks.