I knew early on i didn't want to hassle with all the legalities in MX, so I toyed with the idea of making it legal here first then doing a symbolic ceremony in MX. However, I did not like the thought of doing it twice. I want to say I do to my FH once, and no matter how informal you make the legal ceremony here, it just seems to me it would take some of the 'specialness' out of the MX ceremony (for me anyway).
We are fortunate to have a good friend that is an ordained mininster. We are getting our marriage license here in TX, taking it, along with our friend, to MX and doing a symbolic ceremony there, with him officiating. We will sign our license then and file it when we get back home. My FH has done it this way before w/a previous marriage and it works (at least here in TX).