Looking at a couple other ubiquitous advancing technologies might be instructive. Two examples of advancing technology that have evolved in different directions are Hi-Fi equipment and computers. I think that they've evolved quite differently, and the question is, which path will digital photography travel.
Hi Fi equipment progressed to the point in the large, mass marketing world, until people couldn't detect further improvement, (ie, CD's and inexpensive receivers/players) although the finely tuned ear and test equipment could detect it. So while there are $10,000 pieces of stereo electronics, they are clearly fringe elements. Probably 95% of the receivers sold are for less than $500.
Computers on the other hand, keep getting faster and more capable and we keep buying them. This is because we can perceive the improvement AND it is worthwhile to employ the improvement. So there is immense volume and price stays constant or actually decreases.
I think that a lot of this thread assumes that we'll have the opportunity to have inexpensive 15 or 30 megapixel cameras. I doubt it. They'll only be inexpensive if they are sold in high volume and I think that will only happen if consumers perceive their value. I doubt that will happen. I think that we're closer to the hi fi trail than the computer trail and have just recently reached the point where the two paths diverge.
It will take a few years to look back and recognize it.
Just my opinion.