"...SWA more than likely way over paid for these slots. ..."
SWA has a proven track record of not paying too much for most things. I will withhold judgement though until the purchase price is disclosed. JetBlue paid too much in last years slot deal in LGA, as did WestJet out of DCA. But it's their money and they can spend it as they see fit.
"....and fares in DC increase. ..."
WN has said that they want to use the slots from DCA to STL. I just checked Travelocity and the only nonstop between the two cities is on AA. The fare is $683.80. When fares are posted from WN, we can discuss that. WN has shown throughout 41 years that they will offer a low reasonable fare, good customer service and no nickel and diming of the customer.