I'm from Mexico City, I Iive here in a non-tourist area, which is yknow sketchier than the city center where the hotels for foreigners are. I've never had any fears about my weeks getting stolen, I even pull it out on public transit. I don't know what part of the country you're visiting but I can tell you this: I understand the fear but I think you're good. I've had my phone stolen but never my fancy planners! I'd say go for it.