If you wanted to live in a swimsuit, no one would mind, unless you wanted to go to formal dining in it.
I usually get up in the morning and put on shorts. I've given up doing my hair in the morning because one minute after I step into the moisture saturated wind on the ship, it's a mess. It looks like I styled it with a blender...but you asked about clothes, not hair and makeup.
I wear the shorts all day unless I want to swim. In the evening, I take a shower, style my hair, get dressed all nice and go to dinner. Usually I wear my dinner clothes to the show.
So I count only two outfits a day. Three if you count the swimsuit. You can repeat the outfits if you want. No one cares.
I am a casual kind of girl and jeans and tee shirts are what I wear most of the time at home. I dress for parties, church and orchestra performances but given my druthers, I'd wear jeans there as well.
I tell you this to say it's not like me, but I really love dressing up on a cruise. I love formal nights, dressy casual, the whole thing. I think about what I'm going to wear months in advance. Somehow, it's all part of the fun. If you wouldn't enjoy that, you could avoid it and eat at the buffet. You'd still have a nice dinner, but to my mind, you'd be missing a little of the fun.
It also depends on where you are sailing to. We are doing the Caribbean next year, and I'm planning on two pairs of shorts, four tops and three dresses (for dinner), and two swimsuits. For my husband, two pairs of shorts, four tops, two pairs of slacks for dinner and two swimsuits. That's it. I figure, on sea days, I'll put on my swimsuit, and live in that until it's time for dinner. When we went to Alaska, we took more, because we weren't sure of the weather and needed to look at layering our clothing. There's no need to worry about a different outfit for everyday. Like Marian says, no one will care if you wear the same dress twice or three times to the dining room...
I brought tons of clothes the first time we cruised and I didn't regret it. But I seem to pack a little less each time we go. I get a lot of mileage out of some dressy black slacks paired with lovely tunics and strappy heels. I think what you wear is like everything else on a cruise. Do what you enjoy, have fun, be thoughtful of those around you, and have the time of your life!