As a parent, I think some people are overreacting to this.
First, most people on the DIS boards are super-into Disney and have gone like 20 times and have trouble comprehending the fact that for most people, if you just went last year, you are probably not going to be super-excited about going again. Second, 3 or 4 vacation trips every year is a lot -- certainly a lot more than most people get. So, with the combination of these two factors, it should not be a big surprise that your daughter is rather ho-hum about it. This does not necessarily mean that she is "spoiled;" it means that as a result of her experience, vacations are just nothing very special to her.
Unless YOU really don't want to go to Disney, don't cancel the trip. That's actually giving her more control, and will punish everybody. (Of course switching to a
Disney cruise is out of the question!) The fact is that she will have fun when she gets there. I wouldn't make a big deal out of this; if you harp on it, she might feel obligated to not have a good time!
Some people are acting like she is disobeying you by not being excited, but you can't force somebody to be excited about something! She is her own person and we certainly all know that others don't always feel the same way we do, or the way we think they ought, about things. There is no battle to be fought here.
But, going forward, I would stop with her picking trips. You are creating expectations that may become more and more difficult to meet, and you may in fact be "spoiling" her if the result is that she is unhappy with any vacation that doesn't match her whim of the moment. She has to learn to take what comes in life and roll with it; a kid is "spoiled" when he or she loses the ability to do that. Any trip you take should be a trip that YOU want to take, and you are much better qualified to plan vacations than an 8-year-old.
Of course, I'm a terrible parent. My older daughter (9) is literally the ONLY kid in her entire grade who has NOT been to Disney World. (Although, some went when they were too young to remember.) We're going in a few weeks. You can bet that she is excited!