I doubt you have that much camber (the tires would look "knock-kneed" from the front, leaning way in at the top) from the minimal weight increase. Toe is the biggest determinant of tire wear (yes, it'll change a bit when you add 50-100 lbs to the front but not so much as to wear your tires out).
I'll bet you have too much toe-in. Easily rough-measured with a steel tape and a couple of pieces of angle iron propped up against the tires.
