First I think it's important to define what musicality is. As "musicality" very ambiguously means "the quality or condition of being musical" we need to break it down a bit. I like to break it down into pitch range and cadence. For the sake of simplicity, let's think of these qualities in terms of how you might speak to another person or read a book aloud.
Pitch range
The difference between the highest and the lowest pitch. Very simply this is how big the range is between your highest highs and lowest lows in pitch when speaking. To make the math work a bit better I like to use average minimum and average maximum.
Cadence
Balanced, rhythmic flow, as of poetry or oratory. This is essentially whether your speech follows a pattern or is erratic, and is very similar to tempo.
There is another element that I like to touch on in terms of masculine and feminine voices, though is not a part of musicality. It is the soft or gritty quality that the voice can take on when one is either very gentle and airy or harsh and... also harsh. This quality is helpful in the same vein as musicality and is very much related to glottal attacks and vocal fry which I go over in this post.
So now back to the question at hand, are these things important to transgender voice training?
Well, yes and no. It's actually better to split this into two questions.
Are these qualities necessary for transgender voice training?
Absolutely not. You can completely ignore these if you want to!
Are these qualities helpful for transgender voice training?
I think they absolutely are.
So then what's the point?
Well when we're trying to be gendered correctly, it can absolutely score us extra points to play into the stereotypes of what a masculine or feminine voice is (and if you're trying for something in between, you still need to know your goal posts before you can make a shot for the middle). It can feel a bit wrong actually trying to embody gender stereotypes since doing so can seem counter to many modern movements. Honestly though, we have a hard enough time as it is and if I can do something to have a bit better chance at being gendered correctly I'm going to take that in a heartbeat.
Generally, I like to teach those who come to me seeking a feminine voice to try and imitate a more "high feminine" voice where they learn to speak in a soft musical way with a good amount of range. For those coming for a masculine voice, the opposite is in store with a goal of a "low masculine" voice where they learn to speak in a harsher, sharper and more staccato manner that is more monotone. Though these are usually the goals, it often ends up in a shoot for the stars and land on the moon type of situation where people find a place they like and stick with it. That is exactly the true goal!
Pitch Range Training
My favorite tool for training these qualities is an app called "Voice Tools" that is here for android and here for apple. The pitch, tone, and volume tabs are fun to play around with but the analyze tab is where we will be spending most of our time. You will be presented with a passage, of which you can press the red microphone button then read as little or as much as you want. When you're finished, hit the stop square and you will be taken to an analysis screen. Those seeking a feminine voice would do their best to be very dramatic with their pronunciations, like a sportscaster or radio host, to get a greater range. Those seeking a masculine voice would do their best to speak in a much more monotone manner. A feminine voice would shoot for the difference of "High (95th)" and "Low (95th)" to be from 80-100Hz or 30-50Hz for a masculine voice. While it is not an absolute truth, the trend that masculine voices have a lower range and feminine voices have a higher range is something we can take advantage of.
Cadence Training
This gets a bit wonky because this is very much a social construct. The "high feminine" voice is very much a singsong voice that involves a bit of cadence where your syllables and words are enough in time that they can vaguely resemble a song. The masculine voice is in a bit of a strange place because its role is that it was never taught to be or imitated into having any sort of cadence (unless you were a poet I suppose). The feminine route is to use the same app before in the same way, but with a metronome (here or here for one in a browser) set to around 65bpm to teach you cadence. This should be done at the same time as the pitch range training, and you can even keep an ear listening for glottal attacks and vocal fry to really put it all together. The masculine voice aims to lose whatever cadence it may have, and the best way I can find to accomplish that is to imitate other masculine voices. I wish I could offer more but this is an area I don't know much about, so please feel free to teach me through the discord server!
Happy training!