That's a good point. If the "smooth bricks" are actually porcelain faced you might as well demolish them and put in the color of brick you want. Nothing will stick to porcelain faced brick. Usually those were used in restrooms or some other wet area in the '50s. I thought we were talking about an exterior application.
Most exterior bricks are clay. Different colors of brick are made by using different clays from different parts of the country. This means you would have to consider the ph balance when using any chemicals to stain the bricks. You also must consider any coatings that have been put on the bricks. If the bricks are epoxy coated, for example, you might as well treat them as if they were porcelain faced.
Even if you use the stains from dyebrick, you have to "paint" each brick individually. There must be a threshold of cost effectiveness between replacing the brick and painting the brick. It seems to me that the bigger the job, the more cost effective it would be to replace the brick. Also, you have to wonder about the consistency, durability, and lifespan of the stain. For consistency it would be better to have one person doing all of the "painting", which gets into the issue of time and cost effectiveness. As far as durability and lifespan, I've not found any answers to those. If the stain is a penetrating stain, how deep does it penetrate, how long will it last, does is fade in the sun (is it UV protected), what happens if the brick is chipped. With replacing the brick there is no doubt about what you are getting.
The issue is how much do you want to pay for ease of mind, installation, maintenance, consistency, and a string of other issues. I've just about made up my mind to replace the brick unless I can get a satisfying answer for all of these issues.