quime, I think you are right. Meeting hostel owners is one of the only ways some travelers interact with Spanish people living their "real lives."
Of course you see waiters/waitresses, shop clerks, etc., but they are all "on display" for customers. Hostel owners (and some small shopkeepers) work in their HOMES, and even though you're paying, you're (1) a guest in their home and (2) also (for a little while) a member of the family. That means you get treated well, in most cases, but also hear what the owners really think about things like coming in late! When I stayed at Antonio's Hostal Chelo, his mom lectured us every time we went out the door about being careful with our bags and cameras!
Some of my best travel memories from Spain (and also from other countries, like Italy and Ireland) are of staying in small, family hostels/pensiones and meeting the owners. Even though these people have new faces in their homes every night, they can be so warm and welcoming (I know I can hardly do that with my own mother-in-law!). Some of my experiences:
In the Netherlands, a hostel owner gave us directions to a fabulous "secret" restaurant, and the next morning, cooked us a lovely HUGE breakfast (better even than the legendary big Dutch breakfasts!)--I think because my last name is Dutch and it made him laugh to hear us try to pronounce it "properly."
In Positano, Italy (on my honeymoon), the whole town was closed because it was the low travel season. Our pensione owner cooked us dinner every night (the same dinner his family had) and let his cat visit us in our room.
In Killarney, Ireland, my sister and I were the only guests in a bed & breakfast, and the owner sat and chatted with us over breakfast, telling us all about her family and her town.
In Naples, Italy, in a VERY COLD pensione, the owner brought us a pile of extra blankets and chatted away in FAST Italian for about 20 minutes (we don't speak Italian) about the weather, where to eat, where to shop, etc. I tried speaking Spanish to her, and we understood each other perfectly once she slowed down!
On the Gran Via in Madrid, I returned to a hostel I had been to three years before, and the owner REMEMBERED ME and told me she liked my hair better long (it had been short on the first visit).
There are so many more stories I could tell about the kindnesses of hostel owners. Although you can sometimes be more comfortable in hotels (which may have better mattresses, fluffier towels, etc.), you can't find a warmer welcome than in hostels.
Even the "bad" ones are memorable, if only because there is always something to laugh about (we stayed in one place in Salamanca where they turned the electricity off during the day, and the hostel owner came and yelled at us for trying to turn on a single light to read during siesta time!).
quime, you also have the advantage of being able to speak more easily with hostel owners--I am sure they will all give you a warm welcome to Spain!