SEN obviously does gain extra revenue from diversions, but this would be a minor element of an airport's overall income. I'm sure they enjoy diverted pax sampling the service that SEN can offer as an alternative.
I believe the opportunity is there to make a heck of a lot of money off diverts as they are usually force to pay the published fees. This is not the case for scheduled flights or based aircraft which usually pay a highly discounted fee dependent on frequencies.
This only applies if full passenger handling is required as fuel & go earn little in the way of revenue unless they require de-icing.