Wish I had a new uke every time this comes up.. lol..
Yes, get one. It won't repair damage, but will keep it from getting more damaged, depending on your climate. If you live in a humid region, especially during the summer, it wouldn't have much effect, because all it is is moisture transfer, and if your humidity in your area is equalized with the stellar level that it should be anyway, a humidifier won't add any value. Dryer climates, especially in dryer seasons like winter, of course they will release moisture to try and equalize the humidity to the ambient climate. So, going into summer, it isn't that big of an advantage if any (depending of course on your geographic location).
Anyway, they are cheap, and very good insurance for dryer climates, and seasons. I make my own for pennies, using 35mm film canisters, and clay disks, and moisture pellets. But again, I don't pay much attention to them during the wetter summer months. Many cheap ways to make your own really. Search the term here, and you will have more reading and suggestions than you can read in one evening..