Wheel spacers vs alignment

*Rear* spacers on a live axle won't wear your tires faster in anything resembling normal driving. That's a ridiculous conception. If you track the car, the additional rear track width can cause increased push and also has the potential to slightly elevate rear wear because of the added leverage around corners.

Front spacers can increase tire wear because of the added forces of increased ackerman angle, caster and camber.

Tires already wear unevenly on any car. The fronts do alot of turning and twisting and the rears absorb alot of delivered horsepower. To expect all 4 to wear exactly evenly when they are subjected to different forces is ridiculous. Hence the need to rotate them.

Small spacers in the rear of a live axle car, subjected to normal driving conditions on the road, will not wear markedly faster than the same car without them.

Safety and spacers is a whole other issue. The factory studs don't have a lot of room on them to do spacers, unless they are the proper bolt on kind. maximum I'd feel comfortable with, assuming they are hub-centric, would be about 5mm.