FlyerTalk Evangelist
Join Date: Oct 2005
Location: Ponte Vedra Beach, FL
Programs: DL PM, HH Diamond, Fairmont Prem, SPG Gold, Priority Club Plat/IC Amb, AmEx Plat
Posts: 10,839
What is the fare difference? As mentioned, getting from EWR to JFK may negate any savings. A taxi is the second quickest way to get from to JFK (helicopter via Manhattan being the quickest). Arriving to EWR at 10 AM, you should have time to make it over to JFK with time to spare.
If you miss your JFK flight, DL may reaccomodate you via another DL hub to get you to MCI. Depending on the agent, it could be free or a $50 charge for Same Day Confirm to a different flight (assuming there is availability).