dax,
I worked in mexico.It was a great experience and I highly recommend it to you. you are thinking too much like an American. If you want to go to mexico, just go, and you will be able to do plenty with your EMT. Keep in mind though, that what you will be expected to do, or asked to do, is on par with a paramedic and sometimes even higher level of care. But, down there they are so willing to teach you it is great! Nothing against the USA, but people are not as willing to teach you. So dont worry about that, there will always be someone there to guide you.
I showed up with an EMT cert, and after realizing that what I was expected to do was over my head I went to the hospital to ask to volunteer to learn. I was able to do anything I asked to learn how to do--some people think that it is the wild wild west down there and people dont care about patient care, couldnt be farther from the truth. The difference is they are willing to teach you, as much as you need. They taught me how to suture, start IVs, intubate, put on casts, put in catheters, chest tubes and do an endless list of things. While I was learning there was a doc with me at every step helping me out. Then once I had enough exposure to something they just let me do it on my own. They take pride in doing things well, so you have to really be on your A game, but if you are willing to work hard they will teach you. I learned a lot, which has helped me here in the USA.
I could tell you a lot more about it. PM me if you want.
Also, dont expect anyone to give a crap about it after returning to the USA, everyone here thinks that Mexico is still a thrid world country without hospitals. They will put your experience down. Like it or not, no one is going to really care, so it wont boost you much in your career. Maybe in some places though.
Oh yeah, my Spanish got so good that I was able to run codes and well do everything in Spanish. Best experience of my life. DO IT.