Tbf, noting: In both cases, yes, they're options.
By the time Spain actually replaces those 70 Hornets there can be a viable offer of Marte-ER on Eurofighter. RBS-15 or Harpoon not so much (that's a purely theoretical "we could also fit" from 5-10 years ago, no one ever worked on it). However this would effectively push Spain into a position of a launch customer and sole user, as well as providing a significantly lowered performance compared to current capability. Marte-ER is primarily a helicopter anti-ship missile after all.
Eurofighter ECR is a theoretical develepment option on the "technological roadmap" according to Airbus ("part of a wider long-term capability development plan"). Yes, Spain could buy that, possibly having to extend Hornet in-service times a bit to bridge until it's ready. However development also will take significant investment, and that's something i don't see anyone in Europe having in the next 4-5 years if other options are available.
As for the actual chances of F-35B in the Spanish Armada and F-35A in the Ejercito del Aire and the rumours claiming interest back in November, i recommend
this relatively well-researched article in conservative newspaper La Razon (en espanol) based on information requests to the Spanish government:
La Armada descarta la compra de 25 cazas F-35B y reduce las necesidades a 12 aviones
www.larazon.es
It contains the government clarification that
- Spain did submit a non-binding RFI for F-35B last May in order to obtain information on pricing, terms etc
- The number of aircraft to be procured for the Armada would be maximum 12, not 25 (which had been claimed by Jane's)
- The number of aircraft beyond the Canary Islands replacement to be bought for the Ejercito del Aire would be "about 50". An interest in a partial buy of 25 aircraft (posited by Jane's) is called una cifra filtrada sin demasiada base real (a "leaked figure without a real basis") and fuera de lógica ("without logic").
- The Chief of the General Staff of the Ejercito del Aire clarifies the Hornets on the Canary Islands will be replaced by Eurofighters.
- Quote: "The best solution at present is to replace part of the Hornets with Eurofighter de la versión más avanzada (LTE)" (LTE = long-term evolution)
- For the rest of the Hornet replacement either further Eurofighter (LTE) "or another fifth-generation aircraft" is not ruled out, with the article noting that the Ejercito del Aire traditionally runs two combat aircraft types.
- The article does mention at the end that the Jane's rumour about a F-35A buy were likely placed strategically ahead of certain development decisions for FCAS.