One of my favorite things to do is have my students transpose small pieces and exercises into different keys. This is usually met with a fair amount of resistance. But, I insist, it is one of the BEST ways of really understanding the keyboard. I always say: you want to be able to play in more than one key don't you?
In fact, all my children learn their 5 finger positions ASAP so they can move a simple piece to every major and minor hand position on the keyboard.
I finally made it back to the gym today. I could have done a bunch of isolation exercises on my legs. (These are exercises that work very specific muscles.) Instead of did a few sets of squats. For those of you who don't go to the gym: squats suck. They work about every muscle in your body at the same time. Afterwards you feel like you want to die. BUT they're awesome. You work everything and you get HUGE. (No, I am not a big muscle man.)
Back to piano.
Here's why I brought up squatting. Transposing is like the squat of the piano. (Or maybe the deadlift.) If you select a couple measures with some smarts, you can work your technique, your ear, your understanding of theory, and your musicality. All at the same time.
As they say at the gym: crush it.