Jean Ross of Opening Night Catering has a pretty transparent motivation--that business is located literally right next to the plot in question:
https://www.google.com/maps/place/Openin...4m2!3m1!1s0x0:0x9ecf99c769ecdc63!6m1!1e1
The Allegheny County assessment website says that building is owned by Jean and Harry Ross, and was bought for $80,000 in 1994, and is currently assessed at $150,600, of which the majority is actually land value at $78,000.
So I suspect point #2 (about higher property values leading to higher taxes), perhaps as connected to the second part of point #1 (landowners/small business owners feeling compelled to sell), is the driving concern behind that flyer.
Of course that is classic anti-development NIMBYism--sure development is necessary, and in fact increasing the tax base is necessary, but don't do it in my back yard!
By the way, with all the open lots and low-value industrial properties in that part of the Strip, ultimately it can be whatever we want it (or allow it) to be. Three Crossings is already completely changing the feel of that area, and ultimately there would be plenty of room to do more 15-20 story projects in that area if the market supported them, in which case none of them would look out of place individually.