I think this was a bad idea on Universal's part as well. With guests now able to see it at their own home (minus the effects and moving seats) I would suspect the lines, which are always very high, to take a hit. An even worse idea was to release it with the first Shrek DVD--something many people, such as myself, already own. Remember, at one point, Shrek was the best-selling DVD of all time as well. Even though I think it was a bad decision, I'll still buy the package, mainly because I thought Shrek 4D was pretty good (and this way I won't have to wait in those lines anymore).
As for Shrek 4D holding up.....I don't think it'll last another 2 years at USF. After Shrek 2 is released, there's not much need to see it anymore. And if they make Shrek 3.....forget it. I do hope Universal does the right thing and replace it in the next year or two.