Regarding the language, I don't think Catalan is much of an issue, to be honest. If you talk in Spanish, you get an answer in Spanish. I would say that the climate and the city are well worth it, but I am of course biased, since I live in Barcelona.
I do get the feeling, at least in Barcelona, that the preference is Catalan > English > Spanish. I've only visited as a tourist though; so I don't know how much of that carries over to the business world.
I can tell you that you are highly misinformed if you think the preference is Catalan > English > Spanish :)
Hence, the usual result is that whenever you get spoken at in "broken" spanish you instinctively switch to english. Hell, I've went on to work on tech circles, and I still feel more comfortable speaking english with people who have a strong accent, even if they are germans/whatever and english is not their native language either!
With catalan it is a different situation. Anyone trying to speak catalan is not just trying to survive (they would do that in spanish!). They are actively trying to learn your native language, and it makes you and your culture feel respected by that person. In such a situation, you do your best to try to understand that person and help him improve further without being pedantic.
For a comparison, I've felt a similar "gratitude/respect reaction" when trying to say a few things in Gaelic while I was visiting northern Ireland.
I find that very hard to believe, but if it did happen, it's either a joke or a one-off case.
This is not granted always. It depends on the people.
The problem is that you are trying to learn spanish being inmersed at the same time in another similar language but with different orthographic and grammatical rules. And you see examples of the non-spanish version everywhere in your journey. Should you use a 'B' or a 'V' for that word?. Sounds the same but is often the opposite in the two languages. Lots of people have problems with that without even noticing.
Just to clarify, if you tell someone you didn't understand their initial answer, they won't have any problem changing to Spanish.
Unless you want to pass for the equivalent of a redneck when doing bussiness in lots of American countries and also in most spanish provinces, you should remember that those words must be written in spanish as: alcoba, almíbar, gabardina, abortar, verruga, vivac, automóvil, probar, reventar, verbena, está, China and correr (with word stress in the e this time), for example.
And would be good to remind also that sometimes the same concept is treated as masculine in Spanish but is feminine in Catalán (or the opposite case). Unlike english we use different articles for masculine and femenine words so this is important. Would be like using "she" when talking about our manager John.
And this is only a small part of the complete bobby trap list.