I think some RNG is good, but too much just kills motivation.
Way back in vanilla, re-running the say, UBRS until your shadowcraft dropped was motivating. You'd do the dungeon, hope like hell what you wanted dropped and this kept you coming back over and over. It also meant you'd find groups and a lot of the early bonding in wow was done between "good guys" who would help you farm your stuff after you helped them farm theirs.
When gear with RNG stats just falls out of the sky, theres not quite the same motivating factor. Its still nice and everything, but the motivational feeling is muted in comparison.