I would go with Ireland.
The thing is, if you get married in a place where one of you is from, people won't resent travelling there as there will be some logic to it. If you get married abroad in a place which means all your guests have to travel and there's no obvious reason to do it there except for the fact that you like it, some people are going to be a bit cheesed off at having to fork out so much extra money for your destination wedding.
Personally I think getting married in a country which is not where you currently live is a pain in the arse, even if it's where you're from. But if you get married in a different country to where you currently live, it's certainly easier if it's somewhere you already know well, people speak English and it's not too far away.
Going to see venues, dealing with caterers, menu tasting, sorting out flowers, even the logistics of transporting stuff like your dress over there is going to be a total arseache. If you don't speak Spanish then you will need to be dealing exclusively with people who speak very good English and there will be more chance of things going wrong as messages get lost in translation. You could drive over to Ireland with a car full of stuff quite easily, but getting yourselves and all your gear over to Spain will be more complicated.
It sounds like you've already found a venue and started paying for things in Ireland so unless something has actually gone badly wrong I really would stick with that.
Plus Ireland is a beautiful country and Irish weddings are supposed to be an absolute blast. I would love to be invited to an Irish wedding!
Good luck with whatever you decide.