Boxed sets CAN be way cool. No point in doing a boxed set, and putting two simple booklets and maybe a map or two in them, then you might as well simply put out one or two hardcovers with a map inserted.
However, if done properly, you can add all manner of good stuff, such as specific miniatures, special props (the Tarokka Deck in one of the Ravenloft boxed sets), hand-out and DM maps on nice glossies, punch-out good quality counters, maybe some other physical props as well (hand outs of notes found, seperate hand-outs with pictures to explain what the PC's see), maybe some battlemats, you name it.
Sure, they might be expensive, but if well done, people will buy it. Hey, at outrageous prices, the hardcovers sell like hot bread, why not cool boxed sets? As for expensive to produce... why?? With all the advances in technology, looking at automated packaging companies, I do not see the problem. Only thing is, maybe WOTC (or whomever) needs to team up with a company that already excells at making boxed products inother (i.e. non(rpg)gaming) sectors to ensure quality and low production costs. If 'regular' games such as those from MB etc. can be sold in boxes, complete with all manner of goodies inside, and sell for 30-40 USD, why couldn't RPG-box sets??
It is simply a matter of giving value for money. 'use the box, grasshopper'...