I think your maxi dress would look great! I would bring a light sweater/wrap though to be safe.
I leave tomorrow and the weather looks great, but I took all the advice I see here and packed in layers. I brought some tanks, some tees, and sweatshirts of varying warmth to layer. I also am taking a lightweight North Face to block wind, because I learned the hard way that a very windy day at MK in the mid- to high 60s is BRUTAL and feels much colder.
I also brought shorts, capris that hit mid-calf, long jeans, and long leggings. I am wearing my Uggs down (hey those things are warm!) and packed sneakers in my bag and flip flops in my carry-on because it's supposed to be too warm for Uggs when we get there tomorrow.
I also brought a knit winter hat just to play it safe. Cold ears stink! I went in January twice and we had mid-80s weather and low- to mid-70s at night and it was gorgeous, however both weeks surrounding each trip were mighty cold! So layers for sure!