This is a cruise seriously considering myself. Have sailed on Star a couple of times before refurbishment, one from LA to Miami then across the Atlantic to Copenhagen in 2014. The other from Hong Kong to Singapore, in 2016, where the ship had serious propulsion issues. More recently in October this year enjoyed a cruise on Star from Southampton to France and Spain. Like yourselves I do prefer the smaller ships and Star has many advantages, especially the walk around promenade and open top deck. This means plenty of outdoors viewing opportunities of course, and from every angle, which is great in kind weather conditions or climate, or if you are happy to wrap up well !! The downside is that the lower decks can get crowded including the atrium and bars as well as the corridors. There are windows on the lower deck bars and eating venues but they become very sought after !! Yes, the lack of a forward lounge with big windows and seating is a shame though no doubt that would be busy as well. The ship though felt good, comfortable, happy crew and with a decent choice of bars, food and entertainment.
We cruised the South Atlantic on Norwegian Sun in 2008, including Argentina, Falkland Islands and Chile, and it is the most amazing experience. The scenery and wildlife is incredible. The weather in December was also pretty kind to us. That ship had a lounge forward so if you include the outdoor decks it was ideal. To add Antarctica to your itinerary adds up to a most incredible voyage.
Certainly worth doing on whatever ship I feel however researching other ships and lines is a good idea.