No, but you could be the odd one out if you have dinner in the main restaurant. A few men wear suits, but in the main they wear a tux. Nearly all the women wear long or shorter evening dresses - it looks really lovely and elegant, well worth the dressing up. You could always dine in one of the other restaurants on the formal nights.
No...but why go on that sort of ship and not fit in, you wouldn't go skiing in jeans and a sweatshirt would you?......Nei.
Personally having been on the QE2 I would say you need to dress up in the evenings. Even if it's only a smart dress or a skirt and dressy blouse/top you need to look smart. On the formal evenings most women wore ball gowns or at least a very pretty formal dress (think weddings and your on the right track)
At the time I was only 26 and thus found it difficult on the what to wear front but just invested in some dress and a few ball gowns (try TK Maxx they have stores throughout most of the UK, and you could nab yourself a gown for around £40-60 - bargain!!)
We also have our 18month old with us at the time so it was quite amusing to see my husband in a tux, me in a gown pushing a pram onboard!!
But Cunard is a glamourous line so you should make the effort (or feel a little out of place)
In saying that if you were to choose to eat each evening in the buffet style restaurant I think that's less formal but then you're paying the money so you should eat in the restaurants as the food and service is out of this world.