Hi,
For me it's an awkward one that would have to be explained. I think if you're using the English word 'visit', then people would expect the English spelling of Mexico to go with it.
Radio testing is proving what @bmugford has mentioned:
Name visitmexiko.com achieved 0% radio test score among 23 respondents, being spelled in 10 variants. Worth mentioning that 57% (majority) spelled "visitmexico" instead (the test was conducted among English speaking audience).