IMO, the +1.5 and flipping the front wheels will put the ball joints further inboard and create alot of stress on them, leading to chewing up your ball joints.. just picturing it in my head, but i'd guess the majority of the stress would be put on the upper ball joints, which aren't servicable on the OEM a-arms. have to replace the whole a-arm to swap out to repair a bad ball joint.
the valve stem because it will catch (i think) the arms in a tight radius turn. ripping a valve stem would end your ruin your day and probably end your ride unless you have another set of wheels with you..
ETA: IMHO, even flipping the wheels is putting the ball joints about 2" further inboard than they were designed to operate. takes alot of the stress from centered under the spindle, which would be a vertical stress, and moving it further outside, changing it to a horizontal stress, which they weren't designed for.