^ I really don't think you can claim diazepam to be more addictive in nature than alprazolam, I mean when you look at it medically the drug with the shorter half-life (in this case alprzolam/xanax) will cause physical dependence quicker and generally causes worse withdrawals with cessation than a similar drug with a long half-life.
Personally I am quite experienced with both diazepam and alprazolam, and I like diazepam more, I suppose in this sense you could say diazepam is more addictive to me than alprazolam, but if anything I would wager more people prefer xanax over valium.
I have also never noticed valium fucking up my tolerance to other benzo's, personally I have always used a lot of valium when using benzo's but I never really noticed my tolerance sky rocket until I started eating heaps of xanax bricks.