Actually, if you get rebooked on a VDB often you are rebooked into full Y and get more miles due to the 50% bonus EQM. In fact in October I was bumped PHX-MSP on an award ticket, was rerouted via DTW in Y class and earned over 7K banked miles
Yes, but don't count on it. This happened to me once which was a nice EQM boost, but my last three VDB's they simply rebooked the "flown class", thus no bonus EQM's (though the auto UG was nice).