Yes, what you actually get at the dessert party taken at face value is hard to justify, but you really need to experience both options to really understand.
Here is how I would determine whether you should do dessert
1) Budget conscious? If budget is your main concern, do the virtual queue.
2) Feet start hurting after day at park? Do the dessert party.
3) Don't want to wait in lines? Do the dessert party, although you can wait in line if you want best possible choice of seats. The full meal option is also available to help reduce the wait in line, but not get rid of it if you want best location.
4) Kids. If you have really small kids, it may help to do the dessert party, since they can't see when standing. Full meal option really doesn't help with kids one way or another, except that it may slightly less crowded.
5) Best possible view. You will need to camp out and rush to the best possible location, even with full meal option. Note that the best views has a high chance of getting wet. The dessert party is not best possible view, but it is a guaranteed good view.
Personally, I would not do it without the dessert party, but I only come to
Disneyland 1-2 times a year.