The $400 worth is for a full Epic pass. As the credit and the discount are both a percentage. It's only a 40% off whatever version of the pass I buy.If that's $400 real dollars of credit, I would at least get the Northeast Midweek Pass (essentially free) and keep it in my back pocket.
Granted, the lower tier pass will be inexpensive enough, a further 40% off would make it feels "almost free". But I wouldn't be doing a midweek pass. Partly because I'm not usually able to ski midweek. Also because there's some rumor the Vail is scaling back several mountains to weekend only. If so, it makes the midweek pass rather bad value.