I think I would feel better if I could speak some Spanish but not sure how practical this is.
Honestly I wouldn't bother trying to learn a language for a holiday. It is quite an effort to learn any language to the point where, if you say something and the other person responds in that language, you will understand what they are saying. You could spend dozens of hours on it and maybe have one six-word conversation as a result.
This is particularly a problem with Spanish, where people speak very fast and have a lot of different accents. Imagine if you learned English by reading or listening to the speeches of Barack Obama and then you landed in Newcastle or Glasgow.
Also, even if you do learn to read some Spanish, when you get to Valencia you will notice that most of the spelling on the signs in the street seems weird. This is because the first official language is not Spanish but Valenciano, which is a dialect of Catalan. Everyone speaks Spanish as well, and some "immigrants" from Madrid don't speak Catalan fluently, but they are all used to reading it. Catalan is a cousin of Spanish, a bit like Dutch and German, but they are distinct languages.
I think sometimes that people, especially Brits, try not to be one of "those awful English-speaking tourist who goes abroad and expects everyone to speak English" — but actually, these days, almost everyone you meet in a tourist situation in major European destinations does speak English. For the waiter to speak English to you is as much a part of their service as de-boning the whole fish that they just brought to the table. In fact if you insist on trying to speak your 20 words of Spanish you may actually be making their life harder, because they have to try to understand, and then when they reply in Spanish they have to repeat it four times slowly.
I say this as someone who speaks multiple languages fluently, having lived outside the UK for many years. I also sometimes get the "Oh, try not to be that loud obnoxious English-speaking tourist" thing when I go to a place where I can't speak a word or even read the alphabet. But then I see the Dutch and French and Swedish tourists all speaking English to the Czech or Tunisian hotel staff and I realise that nobody is judging me for being "an arrogant/ignorant Brit/American", they're just trying to get their job done.
Probably the single thing most people can do to improve communication on their holiday is to think about how they speak English and try to make that clearer. For example, "Oi, two more o'those, yeah?" is a lot harder to understand than "Could we have two more beers, please". What annoys people is not lack of language skills, it's lack of politeness and respect.