i do around 2 long haul trips a month, usually via LHR. In the past i have used GIB, and spent the weekend in the town prior to leaving. Unfortunately, the current situation makes it risky travelling through GIB so i drive the hour to XRY instead.
If the situation calms down, and hopefully the Spanish electorate have the sense to dump the current president and his idiotic party, i'm sure GIB can support addition services, pulling more customers from the Cadiz region, im not sure how the airport is advertised outside of GIB, ive never seen much advertising for GIB routes in the last 10 years, outside of the British community, which admittedly is probably the largest market.