I read Altered Traits at the behest of someone here. All I got of it was "I studied meditation for months to reduce my blood pressure, it didn't do anything, so I took some pills, and that was great, but you should meditate."

It seems that all evidence toward any purported positive effects of meditation is extremely speculative, other than "willpower gains" as preached by Kelly McGonigal. The thing is, those can come from focusing on something useful or cardio too.

I can recommend The Mind Illuminated by culadasa. He has a PHD in neuroscience and gives you a very comprehensive framework of how the mind works (with focus on attention) and what kind of improvements meditation brings.