As for cutting back night time entertainment...well as you noted, they already lost the parade since what, October, November? So this event has nothing to do with that. So there is no Wishes those nights, but except for Epcot, every other park closes before MK thought the month. So fig you really needed to see wishes, you can hop back to MK w/o missing virtually anything else.
Then, as for cleaning (LOLOLOL....whatever that meant). The parks are routinely open until 1-2 am in the summer. Same parks, more people/trash....same clean (or not clean) level.
There has yet to be an announcement on a replacement parade for the MSEP. Hard ticket events like this make it less likely that there will be one, since there will be no need for it.
Maintenance and cleaning at WDW is horrendous to be kind. This is not the fault of cleaning and maintenance people, it's management who don't provide adequate time and resources maintain the park to standard it was prior to the mid 90's. Between the parks closing and getting the last guests out, you really cut back this maintenance window. You say an hour or two wouldn't make a difference. when you only have 8 hours of down time, two extra hours can mean a couple of more pieces of trash get cleaned, or monorails get scrubbed, or lightbulbs get changed.