your cabin, D321, is a catagory AB mini-suite. The only place up from there would be a catagory AA mini-suite, which is exactly the same as yours, on the same deck--just a little more midship.
Of course if they offer to upgrade you to a suite, you should jump at it. Just remember there is a difference between an "upgrade" and an "upsell". An "upgrade" is offering you a better cabin at no additional charge, usually when for some reason, they need your cabin. An "upsell" is an opportunity to get a better cabin at a price that is less than the cabin would normally sell for. But I've heard of a couple of instances lately when the "upsell" was just an offer to purchase a better cabin at its regular price. If you want to spend the extra money, fine; otherwise, stay where you are. You have a great cabin
in a great location.