To me, the setup of the oversized spoon, combined with the glass with the teabag is just screaming CHILDREN!!! No adult would do this, and Patsy said so herself in the interviews. I think it is perfectly normal for a youngster to grab the first spoon and glass he/she found and not be concerned with the size of spoon or type of glass.
So JB had a midnight snack! And Burke, with his prints on the bowl, in all likelihood joined her. Patsy's prints are from unloading the dishwasher, IMO. While the pineapple may have been eaten earlier than the midnight estimate, it makes most scientific sense if it was eaten around midnight due to its location in the stomach. Combine this with the first paragraph which suggests children sneaking downstairs for a snack, and the pineapple makes good sense.
As one more point on the pineapple, assuming Patsy and/or John did know about this, I think Becba's response above is right on. Patsy and/or John didn't realize this would be an issue. They gave their "JonBenet was asleep when we got home" story from day one. Once the pineapple came into the picture, they had a problem. But it was easier to stick to the story and plead ignorance. Besides, they got themselves an expert to tell everyone the pineapple could have been eaten some other time.