As a seamstress, I would say you could shorten this dress to a t-shirt, but not to tunic length for the reasons Angie gives. As a t-shirt it would still be body-con, so you'd want to think hard about whether you'd wear that style of top, too.
Certainly, you could shorten the dress, if it's not a length you love to wear. And you might get more wear out of it if you are willing to wear a long cardi over it and add some boots for everyday--i.e., don't reserve it for occasions. I did that with a short shimmery body-con dress I made; I enjoyed wearing it with a long cardi, and with leggings and booties.
