Most of the time I do not bother responding to posts from tourists on travel forums, because sad to say many questions can be annoying and simplistic--it is as if people want answers dropped in their lap (SO easy to research these days!), and they expect their (cultural) way to be the right way.
I am a multilingual world traveler who has lived in different countries, and I learn as much as possible about wherever I am going in advance. Spain has a special place in my heart, so I am always willing to support and provide feedback to interested travelers. When I travel to Spain, I feel like I am in my second home, and I never have negative experiences interacting with people. I have been visiting the country for decades, and I was just there again this Summer in Madrid, Toledo, Segovia, Barcelona, Mallorca, and Valencia, along with swarms of other tourists.
What is a "local'? What is an "attitude"? What does "being welcomed" mean? Do you treat workers like staff/servants, or friends who just have a different job from you? Do you speak only in English and expect everyone to understand you and respond to you also in English? Just spending money does not mean that you have created a friendly environment. I agree the Spanish are getting overwhelmed with non-stop tourism, and may become frustrated with ongoing needs from unprepared tourists.
Yes, the waitress' answer does see a little flippant--I would have had to see what happened during lunch to see why the relationship deteriorated like that. That is not a rehearsal--that is her telling you that she is not going to help you, who knows why.
Your negative experiences are more about you, perhaps, than about Spain and its people.
There is a reason high-level business people take cross-cultural training courses to increase their global awareness and abilities. Spain is its own nation with its own values and traditions. There was a travel campaign at one time that said, "Spain is different." I think that tourists must understand every place is different, and it is we who must adapt as we visit the world.