FYI negative camber by itself will not cause premature tire wear, especially with higher-profile tires with more flexible sidewalls like 50-series or taller. Negative camber combined with toe-out (which happens when most cars are lowered, especially in the front) will absolutely wear the tires quickly. That's why the alignment is so important after lowering - to fix the toe angles. Not to mention there's not much negative camber gain with the McPherson strut type of suspension anyway.