I'm currently doing both Spanish and Economic A-level and wrapping them up in the next few weeks. I've really enjoyed both and I think both can be valued by employers, but I suppose it depends on which sector you want to work in in the future. From a personal perspective (not thinking about what employers would prefer) I would say the following...
Spanish: As someone who wanted to learn another language, this was really enjoyable and I think challenges you in a completely different way than any other subject has ever challenged me. I also really enjoyed learning about South America, as well as Spain, and I really enjoyed the research surrounding my presentation. What I would say, is that because progress is so subtle (but consistent), it can sometimes be daunting, but when you get a moment of realisation as to how far you've come, it is very rewarding and satisfying. So, learning a language is lovely, although as you said above you can always take a language course in the future. Although, it's a beautiful opportunity to now have 2 years to dedicate to learning a language, the opportunity might not come again in the future. The culture was also really interesting, some topics were more interesting than others, (for example I preferred learning about pre hispanic civilizations more than models).
If you did Spanish GCSE, how did you find it?
Economics: I really enjoyed this, and you gain a lot of personal benefit from it too. I think it often explains things that you subconsciously have known and have noticed your whole life but didn't know how to put it into words. So I had a lot of 'ah ha' moments, things I'd always wondered about as to how they worked, and here I was finally understanding them. Although many told me that they found it boring, I had this gut-feeling I would really enjoy it, and I was right I did really enjoy it, so just a reminder that you know best where your interests lie. The biggest thing with economics is that you really really need to understand concepts and ideas (and how they relate to each other) and then you need to be able to apply that knowledge. So, take a biology question for example, asking you to explain the cycle of blood flow through the heart. Firstly, you really need to understand how the cycle works, so that you can then apply it to someone with heart disease, for example. (I don't think Economics is difficult to understand compared to biology, but sometimes, because of this, it's difficult to remember).
If you did Economics GCSE, how did you find it?
So, they both have their pros and cons, like all subjects. I would consider where your greater passion lies, what skill set you hold, what GCSEs you picked and what grades you were working at, if you are planning to do an Apprenticeship or Degree in the future and if yes, what you would then major in, and what your two other subjects are.
Let me know if this helped at all, wish you all the best!