I haven't really had time to look into this, but does anyone know how the up-grades work on thru flights? If I were to book YX 918 from MKE-SFO (with one-stop, same plane service in MCI) will I only have to pay $60 to sit in the "Signature" section? I'm assuming this is the case as the flight number doesn't change, but am not 100% certain.

For those that have up-graded, is the $60 fee worth it?