Barca's is structured differently and not secured against a stadium, but I fully disagree on their income being less stable than Spurs.
They are a Spanish giant, who is ever-present in the CL. Spurs future income projections would be extremely unlikely to reach those of Barca.
Barca earn a whopping 60% more. Spurs are far less likely to be reaching CL spots and approaching Barca in revenue. Barca's CL sport is not under threat. Spurs' source of income is primarily EPL TV rights and matchday revenues. Their matchday revenues won't outstrip Barca's anytime soon, and there's no forecast where La Liga + CL will earn less Barca less than what Spurs make from EPL alone.
Barca have a lot of fat they have to trim but they are also a massive team with more prestige where people want to go and play not just for money. They can pull players on a free (Eric Garcia, Aguero) and some take paycuts to be there (see Depay taking a 30% paycut). They can use that coin for a good few years more before it loses its shine. Spurs don't even have that coin.
Barca also have more young talent in their books than Spurs with De Jong, Pedri, Fati, Garcia, Dest, Trincão, Puig. They have a good young core they can build from. When they manage to get rid of the contracts of Coutinho, Griezmann, Busquets and Dembele they'll be more than fine.