Depending on individual students and their parents. The answer is NO if the students do not think of going to study abroad and financially unable. The answer is YES if their parents want them to learn more English and go overseas.

Students' own motivation is another issue, they want to get out of their present lives and explore the West, or other reasons.

Discouraged students to learn if they do not intend to go overseas and have no interest in English language but have to tolerent the teachers using foreign language to instruct them.

I know it certainly makes it a little easier for a student who learned enhlish in primary/secondary school, to study in an English-speaking country.However, I don't think it has any influence on the motivation. I have met several foreign students that had never learned english, yet are studying abroad. These students, together with those that had the privilege of learning English in primary or secondary had one thing in common, search for means to a bright future. 

A considerable thought is whether the possibility to study abroad motivates students to learn english, or motivates parents to send their kids to english-media schools.

There is no evidence of this in Mexico.  I don't have enough information on Latin America in general, but I suspect that there are not many studies about this. There is evidence however that faculty connections in universities abroad, and their encouragement of their students is one of the most important factors in motivating students to participate in exchange programs or pursue graduate studies abroad.

Do not think this is a big academic question, given China, one of the richest nations and with many millionaires and multimillianaires, their priority is having their children overseas to show they are above others.  The expensive tuition fees and living needs mean most probably, children of those who can afford will go overseas. There are tallent children with less fortunate background can be very much more intellengent compared to their rich friends, carry on with life at home and no bother with English language.

It really depends on the type of instruction they are given (program, module), the amount of time they spend per week in the foreign language class, and the motivation and attitudes of the students in the class. In immersion situations where English is used daily, students might find it really easy to pursue an academic degree in an English-speaking country, for they feel at ease with the language and have the necessary confidence to embark upon such a long journey.