A "wall" is not going to solve the problem, that's for sure. We simply don't have the manpower to guard it. I agree we need to concentrate on keeping terrorists out though, but the money for a wall would be much better spent. Helping the Mexican economy grow would be part of the overall solution too - I'm hoping the next Mexican President finally gets tough on corruption, etc.
On our side of the border, we need to work on the demand side of the equation. Higher levels of legal immigration and especially to make the process easier for qualified immigrants (i.e., the kind of people who aren't categorically prohibited from entering the country) would reduce the amount of needed enforcement by reducing the incentives to illegal immigration. Perhaps we could allow legal immigration at a higher cost to those who are unwilling to wait (rather have them paying the U.S. Treasury than coyotes), so that enforcement resources can be more effectively allocated where needed.
Of course we need to enforce the laws and reduce the incentives that cause the illegals to violate our borders. But we also need to control our borders and they can't be controlled by simply throwing money and manpower at the border. A wall is a physical barrier that can deter most invaders from crossing or at least funnel them into certain areas where we can stop them. A smart wall, one rich with sensors, cameras, etc., is a force multiplier making it easer for the understaffed Border Patrol to monitor and control the border. The wall lets enforcement manpower resources to be used more effectively and allocated where needed instead of having to disburse across every inch of the border.
Remove the incentives and those already here will leave voluntarily as they have no more job, no more freebies, etc. and have no choice but to riot in the streets or get the hell out. And rioting will just bring them out in the open so that they can be rounded up and deported.
Secure the borders at the same time so that once they're out they have to stay out. This has the added benefit of enhancing our national security as terrorists would find it much harder to cross undetected.
Finally, we need to get pretty harsh with Mexico and tell them to get their crap together. This best amigos act is all too one-sided with Mexico reaping all of the benefits of its association with the United States while the average American is getting screwed. Mexico needs to fixed its own problems and if we enable 20 to 30 million pissed off former illegals to go back to Mexico they're going to make some changes pretty quickly.