Being from Manchester I have watched the decline at Blackpool which to me is a very similar airport but perhaps not the catchment area as SEN, the difference
Decline in pax since 2006 - But not in routes. No comparison with SEN as BLK is a niche to a large extent for ex pats and second home owners -This is a strength in a way, as that market is unlikely to disappear.
Lots of good things happening at SEN, feels like BLK 2006 - What easy with new routes though..Jet2 pulled Mahan and Ibiza for no apparent reason, and BLK got Jersey in their place.