https://www.passportindex.org/comparebyPassport.php?p1=mx&p2=us
You could travel to Belarus and Venezuela without a visa, and you can stay a little longer in Bolivia, UAE, and Uzbekistan. That's about the only upside for travel.
For taxes, it makes no difference since you're a US person and subject to income tax on your worldwide regardless of where you live.
Having a second passport is almost never a bad idea, though. Mexico is relatively low profile and neutral.
The only downside is slightly more paperwork when doing things like opening bank accounts. You have to show and declare both passports. So instead of scanning and certifying one passport, it's now two. Not exactly a huge workload.