I’ve been in Spain for 14 years now, has its good and bad sides. Standard advice: people here have mortgages / kids / dogs / credit cards / etc. Same as anywhere else. It’s not (despite bland’s uninformed comment) particularly 3rd world like, and the weather can be cack too. (Although I did manage to get sunburnt today…) Just don’t expect to move and to suddenly find yourself in paradise. That said, I like it here (albeit in Madrid), and don’t feel any particular need to move back to the UK.
I don’t know how good the teaching market is in the Valencia area, it may be harder than you expect to find work. If you’ve got a job offer lined up before heading over that would be a completely different matter, of course. I’d check up on the school before accepting, it probably doesn’t pay holidays, and there’ll be little or no guarantee of work in summer.