I've driven my 4Runner into Mexico twice & my T100 P/U once, but only to the outskirts of Tijuana in the villages (I was down there doing work with a charity).
I always buy my Mexico insurance from AAA. Back when my 4Runner was being financed by a local credit Union the AAA rep just suggested I inform the credit union of my plans to take the vehicle into Mexico though I never informed the credit union, nor did anyone else that was in my group that I'm aware of.
As far as driving in Mexico goes, again I've only traveled in and around Tijuana and into some of the smaller villages therein. DO NOT bring a firearm! Don't make your vehicle look too American. My trucks have CB radio's, Sirrius satellite receivers. First thing I do when I get parked is to hide all that stuff.
Don't wash your T4R for a couple of weeks before your go, it's better if it looks a little "weathered". As was mentioned previously add wheel locks, secure your spare, when I'm down there it's generally to assist with a home building or improvement so I make sure to park within sight of where I'll be working.
Tinted windows are illegal in Mexico and at least in and around Tijuana the Federales are really looking for it. That having been said both of my Toy's have light tint on their side windows, I've driven both down there in the past 12 months and have had no problems. Also talking on a cell phone is outlawed, I don't know if headsets are allowed, navigating Tijuana is a white-knuckle experience for me and my phone generally doesn't work until I'm in-line to come back into the US.
Limit the amount of cash you carry on your person; don't carry a wallet, rather carry DL, insurance info and some cash (small bills) in a pocket. I've never had to pay a bribe but know of people in the group I volunteer with who have.
Carry whatever you need to keep you and anyone else you're traveling with running. Buy gas before you cross into Mexico. I don't carry extra gas (again, I don't drive that far into the country). I also make sure my spare tire is in good shape, jumper cables, standard fluids, etc. like you would carry for any road trip.
All that having been said I've never had a problem with corrupt Federalies or theft, in fact I've found the people to be very friendly and accommodating.
Have fun!
--Kevin