Hey this is great!
That's the way I love piano solo. With tempo and velocity dynamics, cantabile, and as you said there is no better way to do it then playing it live on your keyboard :) I think it's the best way to connect with the sounds too, when you play live I'm pretty sure you fall in this kind of "trance" bubble easier then when you compose note by note :P
This technique is good for multiple tracks compositions too. Once your improv is done you can correct some mistakes, then you can copy your midi track to another instrument, remove all the notes you don't want this instrument to play, and you have a score timed perfectly with your improv. Then you can change the notes to make the other instrument play 3rds or 5ths or whatever. It makes a multiple track song sound a lot more human than when it's composed note by note, because you keep all the natural dynamics from when you played it.
Good improvisation, I love this wet reverb too, it gives a nice hovering feeling. I'll try this kind of reverb on my next piano song :)
5/5 10/10 Carry on!