I personally think that we should inspect the cars more because we probably haven't checked certain areas in a car that could possibly contain drugs or bombs waiting to go off, for example we check glove compartment and the back of a car but we barely chack between the hood where they could of smuggled something while the car was being built (sources say).
I have personally been through borders and I think they check enough. For every car that passes by, they use an X-ray machine to check the cars. they also peer in the car, and check your background. It would be such a hassle, waste of time, and waste of money to check thoroughly every single car. Especially, because not every single person wants to smuggle drugs, many people just want to visit family, visit locations etc.
When I mean cars I don't mean just cars I mean automobiles in particular. You are right it does take a little e bit of Time but it is worth it because it could save a life or two. Also if you own a vehicle do you worry about what might happen to it I'm sure the answer is yes you do. What if not even a day after you got the car and the minute you leave it it just blows up. That is just an example but it could happen.