Priority Boarding essential if travelling with kids or elderly in peak season or weekends. Not that essential if just 2 adults but get in Q early all the same.
Also , as plane fills up they tend to be more particular with the carry on bags at end of Q. On the other hand your flight might have a large group of Spanish or Irish students in which case €4 for priority could be money well spent. Either way with or without students a pair of ear muffs or MP3 player would be useful as Ryanair flights are not exactly relaxing experience.
If booking well in advance or Irish Bank Hols try Iberia via Madrid for a more civilised experience,an all-in price and 23kg check in luggage allowance.
Been to Seville Aug 2008 and found it a beautiful city easy to get around on foot. Small easy airport. Lack of Taxis out at the theme park though.