The vouchers you would buy would be good. But say the canceled the discount next month you wouldn't be able to purchase them with the discount anymore.
You can always find ticket prices on this site by clicking Theme Parks at top of thread page and then find and click Park Tickets. The price is provided without the 6.5% tax, see http://www.wdwinfo.com/wdwinfo/tickets.htm#ap
Nope. Perks are not part of your membership. What you're buying is the right to stay at a DVC resort, subject to availability. Everything else, from the AP discounts to the ability to use points for DCL, can change or go away the day after you buy.
Most of the discounts are offered by third parties. The AP discount comes from Disney Parks, another division of the Disney company, and they can take it away at any time.
Just to give an example, free valet parking was taken away overnight with no notice. Members valet parked one night thinking it was free and when they picked it up the next day they had to pay. Disney outsourced valet parking to an outside company and they decided not to offer it to members free.
There is no such thing as a "DVC Discount" related to any Annual Passes (No matter what Member Services says).
There are two separate categories (or price ranges) of Annual Passes. The lower price range is for Florida Residents and for DVC Members. And the higher price range is "Tourist", which is people who do not qualify for either of the other categories.
And of the six possible DVC Member AP types, the price difference ranges between $115 and $149.
Regular and Premium Annual Passes have the same privileges, no matter which price range they are in.