Adding a CAI can add power. However you need to do it right. Just moving the MAF to a larger tube won't work and lot's of people find it better to keep the stock intake snake assembly rather than making their own just because they don't have a way to tune the AFR.
This adapter mounts the MAF in the exact same way as stock making it read the exact same value. The open airfilter and less restrictive intake will up the air flow without changing the MAF calibration.
Reading about the MAF mod, I can not really see why that would make things better. Sure you remove the vanes giving a little better air flow, but still sucking air through the stock snake.
In my mind it makes more sense doing it by removing the snake, adding the Superhero adapter making the engine get colder air with way less restrictions. Going larger injectors yada yada will not improve stuff unless you are maxing the stock injectors out. Which I assume we are not doing looking at my wideband O2 sensor.
You should go back and carefully reread the Cap's maf mod thread.
That being said, TRD did make a non velocity snake that cost a gazillion dollars. Completely removing it will only pull hot air from the exhaust side. The behind the battery approach is appropriate but I believe it should use a block off shield or an airbox.