I like the somewhat grainier texture (Not true marzipan) that you get in quality almond croissants, similar to these:
The ones I make at home (rarely, and I use purchased croissants, but these are the afterburners of heartburn!) I use a coarser ground almond meal (grainy, as I said) and yes, cinnamon though with a very light hand.
I do think the marzipan stuffed dates would be wonderful, but I’d -have- to add an accent flavor to cut the sweetness (or just make less-sweet marzipan). I mean, I’ve done stuffed dates where I used a lovely smoked mozzarella and was super happy, but dates are plenty sweet on their own.