I always prefer to buy a la carte. I book my rooms through the hotel and buy my admission shortly before the trip. It is generally VERY easy to cancel a hotel room booked through the hotel, even if you cancel just a couple days in advance. But there may be issues with getting your money back when you book a travel package. Of course you could buy
trip insurance, but since I usually drive to get to the parks (or else fly Southwest, where you can get your credit back even with late cancellations) it doesn't make sense for me.
In other words, I'm a control freak, and/or the type who likes to have the OPTION to get out of even delightful things (a trip to Disneyland) should the need arise, so booking separately seems to work for me.
If you buy your tickets at the last minute, the price may go up between when you decide to take the trip and when you go, though.
I THINK I read a RUMOR somewhere that people who book vacations through Disney MIGHT get special seating or standing space for World of Color. I'm not sure that's going to be the case, but IF that happens, then booking through them might be worth it, provided your party is big enough and the cost isn't too high. (There will likely be special seating and standing space that can be reserved and purchased in advance too. One rumor is that if you spent a certain amount of money at certain restaurants you would get guaranteed standing space, which might not be an awful deal. But if you're a party of 2 and it would cost $300 more to book through Disney, then I like to think you would be able to buy reserved seating for cheaper than your package price.)
Anyway, I certainly wouldn't buy a package just because there are rumors that it might help you see a show, but I thought I'd mention the possibility.