There's one point you missed on the V-6 and V-8 Monzas. Maintenance. We got a V-8 version at the salvage yard I used to run. It had really high miles and the valve seals tended to foul the #7 spark plug. To change that particular plug (#5 on a 6 banger) you needed a special tool, only available to dealers or you had to lift the engine out. We got around that with an inner tube, some snaps and a really really long socket extension. One of the guys bought the car from the yard and every 200 miles or so, he would turn the wheels all the way to the left (I think, it's been 30+ years), pop the plug wire off, remove the piece of inner tube and zip the plug out and the new one in. Hook the wire to the new plug, cover the hole and he was good for another couple of hundred miles.
These cars, and the related Sunbird, are still popular with hot rodders. If you can find a TH200 transmission, you can drop a V-8 in an originally 4 pot car.