By my best guess, the fumes and heat problems on the 2013s could be fixed for less than $5k per bike, including labor. Yes, a tidy sum but cheaper than buying the bikes back and they could likely bring the parts cost down by a number of means.

New body panels and air cleaner assembly to move air through the engine bay.
Ceramic coated header pipes.
double wall insulated fuel tank.
Relocate the charcoal canister ala 2014s
Reverse flow cooling fan at low speed or stopped ala 2014s

Even if they did all of this, its not the end of the Spyders financially. but I dare say, IF they did all this, the 2013s would be nearly as good a bike to ride as the 2014s except for the torque and fuel mileage of the ACE.