I'm sure everyone has different opinions on this, I think it depends on YOUR one year old, kwim? If you think it would be reasonable and enjoyable for her...of course, it is hard to tell now, she isn't born yet.
I'd go ahead and book it, you can change it later if you decide it will not work out. The price will only go up.
Both of my children cruised as one year olds, and had a great time. On our most recent cruise (2 weeks ago, lol) my DS was 4 and DD was 2, and it was so fun. I think it is so magical at that age, they really believe it is Mickey they are meeting, ya know? And it is a nice family vacation for us, there is so much to do without a ton of work or planning on our part, meals are included and will be served just a deck away, and no cleaning for mom. Gotta love it! DH and I also get a little bit of alone time, which doesn't happen on land vacations. My DS loves the club and DD has enjoyed Flounders. We usually only take her in the evening (after dinner) and she will fall asleep there. Yes, it is $6 an hour, but well worth it (and much less than we pay for a sitter at home!)DH and I will have a meal in Palo and also go to the spa, but other than that we are all together.
There's plenty to do for the young ones, you just have to work around their schedule. Try to keep the regular nap time and bedtime, and usually they are happy.
We just have different expectations, we sort of chill out a lot and go with the flow. The kids are too young for all of the excursions, so we often stay on the ship and play at Nassau. The splash area for the babies is perfect (on the Wonder), my DD could have stayed in there all day. She enjoyed lunch up on deck 9, looking out over the water. Last year, she was almost 14 months when she sailed, and it was the same. The littlest things would be fun for her. Walking around the ship and looking out the windows, riding the elevator and seeing the big mural of Ariel, having ice cream with lots of sprinkles...LOL. She also enjoyed the shows, there's lots of singing and special effects (although she would sometimes fall asleep before they were over).
I would much rather take a one year old on a cruise than go to WDW. BTDT, not fun. But a cruise can be enjoyable for the whole family. I wouldn't NOT go on a cruise just because my child will not remember it. Maybe if it was going to be a once in a lifetime vacation...then I'd wait until age 4 or so. But if you are just looking for a good family vacation for next year, I think a cruise would be great. We have vacationed with our kids since they were small babies. They might not remember it all, but I do. And I have some fun family pictures and videos to share with them later. I'm not going to just stay home until they will remember things. Of course, any beach will just be a beach, they may not appreciate that it is
Castaway Cay, or that they got there on a big boat...but they will have fun just the same. And your older son will have a blast, he will be a great age for it.
So, this is getting a bit long.
I'd say that it is worth the extra effort it takes to travel with a young one. If you have any specific questions, especially when it gets closer, this is the place to ask.