Dbat, our ds12 has dysgraphia that's due to Developmental Coordination Disorder (fine motor related), and typing is also very slow for him due to the DCD. However - it's faster than handwriting and he does get *some* of the benefits of a reduction in drain on working memory when writing (over handwriting). Like geofizz, when our ds was first diagnosed, the recommendation from his neuropsych was to teach him how to type first, then move him to voice recognition. One thing you can do with typing is to *not* insist that your child use traditional touch typing, but instead let them figure out their own version - it's ok if your child chooses to only use thumb and first-finger for instance. Also get them to practice as much as you can (this was a challenge for us!).
Re the piano - our ds actually plays piano relatively well and enjoys it... but his finger position looks odd and the joints in his fingers sometimes bend backwards... so it's a little weird! There are some children who have a vision challenge as a component of their dysgraphia, and just fwiw - my dd who had a vision challenge had a really tough time learning how to play piano until we had her vision corrected. Just something else to consider (as if any of us needed anything else to consider lol!).
Re Dragon - we had a tough time the first time around with ds when he tried to train it. We're giving it another try, this time having him read his favorite stories to it for extended periods of time, then going back and making corrections (this technique was recommended to us by a group that works with helping clients with disabilities use Dragon etc). Our ds also prefers the free Dragon app on the iPhone/iPad - you have to be online to use it because it uses an voice recognition online database, but the cool thing about having that online database is that it draws from soooo so very many voices (from what I've been told) that it is really good at voice recognition, no matter who is talking. It's also fairly forgiving of background noise - so it might be something else you could look into. We used to let our ds use audio-recording too, and he was allowed to turn in assignments that way (he used Garage Band on the Mac). And... fwiw... I still scribe for him quite a bit for homework, since his typing is so slow.
FWIW our ds had a low score on the NEPSY fine motor tasks; his lowest scores were on finger tapping, which is a symptom of fine motor dysgraphia.
Gotta run - hope that made sense!
polarbear