Dept. of State Foreign Service Institute classifies native Spanish speakers as level 1 degree of difficulty to learn English because of the similarity of the two languages (many Latin roots for words in both languages). Level 1 also includes Italian, French, Romanian, Danish and Dutch.
Level 2 (somewhat harder) includes native speakers of Slavic (Polish, Hungarian, Russian), Indian (Hindi, Bengali), Southeast Asian (Vietnamese, Thai), and even Persian languages and Zulu. Greek, Hebrew and Tagalog are also in there.
Level 3 (hardest) includes Japanese, Korean, Chinese and Arabic.
I know a LOT of people who are native speakers of Level 3 languages who have pretty much mastered English, albeit with an accent, and most of them learned when they were past college age via immersion in the US or the UK. I also know some people who live and work in local Vietnamese, Korean, Polish and El Salvadoran neighborhoods who've been here for years and can barely speak or understand English. It ain't that hard to learn English if you're a native Spanish speaker and I wish a lot more of them would do it to change the perception of those bigots out there who think Latinos are dumb.
The problem here is the same old separatist mentality that's hard to shrug off: if you have a chance to be with people who are speaking your language and making you feel comfortable in a strange place, you naturally flock to them. Increasingly, kids in public schools can speak another language besides English everywhere except English class.
Until there is greater immersion into the English speaking world outside of the comfort zone, it ain't gonna change. I agree that there needs to be a lot more incentive to learn English.
Having English as an official or national language may facilitate public schools enforcing an "English only" policy in the classroom (except where counter-productive, ie: foreign language instruction), but eventually it'll be left up to the local school boards to decide. School boards are made up of politicians, politicians need votes to be reelected, some communities may not be hyped for English Only policies, politicians will reflect that in their actions to ensure reelection, yadda yadda.
JV