Please do not worry i am sure that your outfits will be fine i have travelled Cunard many times & found that the older ladies dressed with grace more than style wear sensible shoes as it is a very big ship with lots of walking you will love the ship .
First of all you have made a wonderful choice and should concentrate on thinking on how much you will enjoy the experience rather than on your `finery` which I am sure will be great. The major differences are that QM2 was built as a liner not a cruise ship and that atmosphere comes across and most of the people that travel on her recognise this rather than perhaps recognising the atmosphere generated by other lines which may be more akin to Centre Parks or in some cases Butlins. They are catering for different markets and different requiremnts eg if I had a young family I would go RCI and not Cunard but if I want to dress for dinner and a more elegant atmosphere I would go Cunard and if I wanted an older atmosphere I would go Fred Olsen or Saga and if I wanted meat and two veg and saloon bar at the pub I would go P&0. It is all about horses for courses but don't be put off Cunard you will have a wonderful and elegant time I am sure.
We went on the QM2 in January. Formal nights - some men in Tux's some in smart suits. Some women in trouser suits some in gowns. Don't worry, as long as you look smart anything goes. Black evening trousers combined with some colourful soft tops, a bit of bling and a scarf can look stunning. So just go and enjoy yourself and don't worry.