would you ひく a marimba/xylophone/glockenspiel, because it's a keyboard instrument? or would you たたく a marimba/xylophone/glockenspiel, because you play it with mallets/sticks? or would it be a different verb?
I think in this case you would use たたく because as you already said, these instruments are played with sticks. たたく literally means "to hit", hit with a stick, as you do with drums so it would fit the best I think. I hope you understand what I try to say.
I agree, normally a marimba is struck 叩いた; however, if you are describing a particularly moving and lyrical performance, I don’t think pluck 弾く would be out of place.
By the way, if you are interested in marimba, you’ve got to check out Fumito Nunoya. I was privileged enough to see him live, and he’s just amazing.
Actually looking up examples of people playing the marimba, both 弾く/ひく and 叩く/たたく get used, but 叩く seems to be used more when specifying how it's played (i.e. with mallets) than for someone making music.
But it looks like 演奏する/えんそうする ("to perform music") is by far the most common way to express it. マリンバを演奏する.
I agree, normally a marimba is struck 叩いた; however, if you are describing a particularly moving and lyrical performance, I don’t think pluck 弾く would be out of place.
By the way, if you are interested in marimba, you’ve got to check out Fumito Nunoya. I was privileged enough to see him live, and he’s just amazing.
i just visited fumito nunoya's website and listened to him play, and he'll be a big inspiration to me in my marimba learning
たたく literally means "to hit", hit with a stick, as you do with drums so it would fit the best I think. I hope you understand what I try to say. 
