For a vacation, the best way to work Priceline or Hotwire for airfare is to consider your travel days a total writeoff, rather as if you were driving. If you NEED those days to be part of your vacation, then you are better off not doing an air auction, unless you can auction a pkg.
So, if you want to take a 5-day, 4-nite WDW vacation, plan to be gone from home for 6 nites. As an example, if your vacation is Saturday thru Wednesday, you should plan to fly down on Friday and fly back on Thursday. Calculate the extra time off work, if any, into the price you are willing to pay.
These services work great for rentals and hotel nights, but not nearly as well for air tickets. Not only are the times sometimes bad, but the ticket restrictions can be brutal. I've only bought air tickets once this way, and due to a situation with airport security, we missed the outbound flight. Because we bought it on HW, AA would not less us standby for it: it cost us an add'l $1000 to get on another plane for that trip, and that solution was only offered after we spoke to 3 supervisors with our sobbing toddler in tow, and essentially begged for all we were worth. (The trip was to California.)