Wear what you are comfortable in. If your DH is not used to wearing a jacket and tie, don't force the issue. If I would have forced the issue on my DH, he would have been uncomfortable and miserable, which would have wrecked our evening.
Our compromise on this was - DH wore a nice pair of pants, a shirt and an awesome Disney tie. The advantage was - we didn't have to pack a jacket, which would have taken up too much room in the luggage. At Palo, I don't even remember what other patrons were wearing - I saw nothing that wrecked my evening there - either from a "we're not dressed up enough" or "we're dressed up too much" point of view.
My outfit was a really fun, dressy 3 piece thing that had a split skirt. I certainly hope the fashion police wouldn't have mistaken that for shorts.
The most important thing is have fun and stop worrying about what the others will think of your outfits. That will wreck an evening faster than anything.
If it makes any difference - we where on the Wonder, so didn't have to worry about formal night and semi-formal night.