In many ways, its all relative. Even on the most spectacular built up course, if every hole is visually or otherwise spectacular, don't all become somewhat bland by virtue of being nearly equally spectacular? There is certainly sensation overload on several signature courses, and a bland hole would perhaps help that, as well.
It has been touched on, in terms of ebb and flow, but yes, a few holes may need to be bland to make others stand out. Hopefully those are holes that some natural slope means you don't need to use a lot of hazards, and thus, it seems bland, but can play hard, or at least tricky, interesting, etc.
I don't see the trend toward visual spectacles reducing. Any architect who gets a chance to build a new course will at least be tempted to make it a masterpiece (as opposed to when you might have 3-5 new courses a year) In bigger terms, if my generation was the TV generation and appreciated visuals, so does the younger generation, but add in the movement and constant excitement of the video games they played as kids, and something tells me, the next generations may subconsciously need non stop action to really enjoy golf.......