On both issues - treating vouchers as a discount and affording VIPOW's lower priority than miles - I think AA shows an unfortunate predisposition to bite the hand that feeds them. In the case of vouchers the airline has asked you to do them a favor -help them out in a difficult situation that they are responsible for in return for the voucher. If you help them out it seems foolish to devalue their thank you - it leaves a bad taste in the mouth rather than leaving you happy that you helped out.
As to the VIPOW's which are rewards, awards, given only to AA's very best customers - it is inconceivable to me that AA would then turn around and devalue this award. Other than the absolutely marvelous ExecPlat desk and the rarely observed 72hr e-upgrade clearance there is precious little that AA does for its explats to distinguish them from the lower tiers. Although I can understand the rationale for preferring first money then miles then other forms of payment it seems that the loss of goodwill amongst AA's most dedicated customers simply does not make sense. At a minimum AA owes it to its best customers to make it very, very clear the relevant priorities. I, for one, would not want to lose an upgrade opportunity at certain simply because I didn't know the pecking order. As a very frequent AA traveler I always have enough miles to pay and would hate to lose the opportunity.