Everyone is entitled to their opinion. I don't see the 73 Mach 1's being all that collectible and the tire change can be reversed in a matter of minutes.
Since I already updated the transmission to a 5 speed, added a solid cam and closed chamber heads, an electronic ignition and intend to add air conditioning and subframe connectors to the car, it won't be an "Original" to most collectors. Still, there is nothing I've done that can't be reversed. If I should need to trim the inner lip of the wheel well (which seems unlikely) even this is a reversable modification.
I didn't buy this car as an investment, I bought it so I could enjoy having it the way I want it. If that makes my car a restomod, I can live with the title.
I fully respect your opinion and there a great number of cars I would do as you suggest and keep as original and stock as possible-which is exactly why I don't own one of those cars.