The laws may have changed but what is permitted is well published by the Mex. govt as well as some accurate info here. Have not heard about fish. Beef and beef products, like dog food are on the no no list and the amount of alcohol you can bring in is restricted. Nothing new about any of this. And yes the Mex. govt does not feel it is necessary to inspect each and every vehicle coming into the country and it depends on which agents are doing the inspection. Everyone is just doing their job and passage has been uneventful for most.
Dont' be a fuss budget just enjoy the Mexican beers, there are quit a few. Really all you need to bring is some clean skivvies and a couple of changes of clothes, swim suit and cash. You can find anything you need here and no fuss over packing a lot of crap from up there.