Although we did end up living in hotels because if you want to relax, you need room service! Or else, you'll end up doing everything yourself and that's no holiday.
But of course, if you are going on a one month vacation or even a 2 week holiday, some of the rental apartments are very good, exquisite in safe neighborhoods (you can select your area) and they are way affordable than the hotels.
Two websites that are very useful, if you are looking for short term rentals are www.friendlyrentals.com & www.spain-select.com (Spain Select is more upscale luxury apartments and Friendly Rentals is all quality matched with price).
Below are photos of general Spanish interiors, out of which some are short term yet stylish! (Surely I wouldn't want to be back if I lived in such apartments, I guess secretly that's also a reason I decided to go with a boutique hotel).