Renting a car in D.F. has all kinds of risks associated with it. For the most part, public transport is safe in Mexico, just don’t flaunt expensive belongings (cameras, watches, designer clothes, laptops).
Of the people I know who have gotten robbed in Mexico, most have been either at the airport or in traffic (in a stopped car)….both in broad daylight and with plenty of people around.
Also, Mexican drivers take traffic lights, stop signs, and speed limits more as suggestions than actual regulations…yet another reason not to rent a car in Mexico.
I would suggest checking out a “tour” company at your hotel in D.F. They can arrange for a private bus to pick you up at your hotel. It will be more expensive than public transport, but you (and the hotel) will have an audit trail of where you’ve been, and who picked you up. Kidnapping is a serious problem in Mexico City.
After you check in, go for a late taco/queso fundido. There are some great quality trendy late night open air eateries around Polanco and La Zona Rosa. Lots of beautiful people around eating great inexpensive food.
Depends on where in Palo Alto and if you want to walk around or drive to sites/attractions….and what businesses you are visiting. If you stay near University Ave in Palo Alto, you are within walking distance to a plethora or restaurants and shops. Otherwise you are driving to get to just about anything.
If you are looking to not drive into San Francisco, you can take the Caltrain right from near University Ave, into downtown SF.
Other cool “downtown” areas on the Peninsula that have the same kind of attractions as Palo Alto and easy access to SF are Burlingame, Melo Park, and Mountain View. What Palo Alto has going for it is Stanford University.
Palo Alto is pretty central to anywhere in the Bay Area with the exception of North of the Golden Gate or the Far East Bay (Concord, Antioch, Pittsburg).