Dear Ann -
I simply relegate DH to swimwear and gym short and use all his leftover space!!
Seriously, I am also of the "use your alloted luggage quota" school but have found that for us on the cruises, I didn't use all that I brought and it's a pain to repack so I've cut back. Here are my suggestions:
#1) We enjoy dressing up so I bring one long formal, one dressier dress (semi-formal night) and I also bring a Tuxedo pantsuit. Those and DD's (8 y/o) dresses for Formal and Semi-Formal nights go in a hanging bag. Over each of our individual dresses I hang a separate plastic dry cleaners bag which helps a lot with decreasing wrinkles.
#2) The rest of the dinners I wear dressy or casual pants depending on theme with different sweaters for mix and match. I can also wear the pants during the day just by wearing a different shirt or sweater. I dress them up or dress them down depending on the sweater and jewelry. The pants and sweaters fit nicely in the suitcase.
#3) I pack one large suitcase for DD and one for me with outfits pre-planned for each day and/ or evening. Sometimes, it's just a pool coverup and swimsuit or shorts and a tee-shirt. It sounds funny but doing that cuts way down on the amount of clothes we bring. Most importantly, this method successfully leaves room for new purchases!!
One note: I ALWAYS bring "little girl plastic hangers" and adult hangers along and then we maximize use of the closets and store nightgowns, underwear, bathing suits, cover-ups etc in the drawers. I also leave the adult hangars from the dry cleaner on the ship for more room on the return trip.
#4) I take the minimum # of shoes (just cause I hate packing them): Dressy black pumps, simple black leather heels, one pair of Sketchers and pool shoes. I find that I wear the Sketchers and pool shoes through most of the trip but running shoes with a long formal just don't work for me.
If you enjoy dressing up, I think you are very smart to rent the tux for DH. It works well and saves a lot of room. I don't think DH will wear it more than two nights (Formal/Semi-Formal) unless you would like him to wear it to Palo's. From what I have seen, most men didn't wear tuxes on Semi-Formal night but my DH did and he was very comfortable. And, to be honest, our pictures from Formal night were simply awful and the ones from Semi-Formal were great so we are glad he wore it the second time.
Have a wonderful cruise.